/* =========================================================================
   HL PhysiQuiz — Feuille de style unique
   Palette sémantique + thème Clair / Sombre / Système
   -------------------------------------------------------------------------
   Une seule feuille de style. Les couleurs ne sont jamais écrites en dur
   dans les composants : elles passent toujours par une variable sémantique
   définie ci-dessous pour le mode clair, puis redéfinie pour le mode sombre.
   ========================================================================= */

/* -------------------------------------------------------------------------
   1. PALETTE — MODE CLAIR (valeurs de référence)
   ------------------------------------------------------------------------- */

:root {
  color-scheme: light;

  /* Fonds */
  --background: #f7f5ef;
  --background-glow: rgba(75, 155, 194, 0.16);
  --surface: #ffffff;
  --surface-secondary: #f9fbfc;
  --surface-raised: #f2f6f8;

  /* Textes */
  --text-primary: #17202a;
  --text-secondary: #607080;
  --text-heading: #0d2b44;
  --text-on-accent: #ffffff;

  /* Traits */
  --border: #d8e0e6;
  --border-strong: #b9c7d2;
  --panel-border: rgba(21, 59, 91, 0.1);

  /* Accent */
  --accent: #1f6f9f;
  --accent-strong: #175d87;
  --accent-soft: #e8f4fa;
  --accent-glow: rgba(31, 111, 159, 0.25);

  /* États */
  --success: #237a4b;
  --success-bg: #e8f6ee;
  --success-border: #bfe3cd;
  --error: #b23a3a;
  --error-bg: #fbecec;
  --error-border: #eecccc;
  --focus-ring: #e9b949;

  /* Sélection d'une réponse */
  --selected-bg: #d9effb;
  --selected-border: #1974a8;
  --selected-letter-text: #ffffff;
  --letter-bg: #edf1f3;
  --letter-text: #153b5b;

  /* Bandeau et pied de page */
  --header-bg: #153b5b;
  --header-text: #ffffff;
  --header-rule: #e9b949;
  --header-control-bg: rgba(255, 255, 255, 0.14);
  --header-control-border: rgba(255, 255, 255, 0.28);
  --header-control-hover: rgba(255, 255, 255, 0.24);
  --header-control-active-bg: #ffffff;
  --header-control-active-text: #153b5b;

  /* Encadré de score */
  --score-bg: #153b5b;
  --score-text: #ffffff;
  --score-label: rgba(255, 255, 255, 0.78);

  /* Barre de progression */
  --track-bg: #e8edf0;

  /* Boutons désactivés */
  --disabled-bg: #e1e5e8;
  --disabled-text: #7b8790;

  /* Ombres */
  --shadow: 0 18px 50px rgba(17, 47, 70, 0.12);
  --shadow-soft: 0 6px 16px var(--accent-glow);
  --shadow-card: 0 2px 10px rgba(17, 47, 70, 0.05);
  --shadow-card-hover: 0 12px 28px rgba(17, 47, 70, 0.12);

  /* ---- Pastels sémantiques HL PhysiQuiz (blocs de cours à venir) ---- */
  --pastel-definition-bg: #e9f2fb;
  --pastel-definition-border: #c3ddf1;
  --pastel-definition-accent: #1f6f9f;

  --pastel-formula-bg: #fdf1e3;
  --pastel-formula-border: #f2ddc2;
  --pastel-formula-accent: #a5651a;

  --pastel-method-bg: #e8f6ec;
  --pastel-method-border: #c6e6d2;
  --pastel-method-accent: #26794a;

  --pastel-example-bg: #f0edfa;
  --pastel-example-border: #d9d1ee;
  --pastel-example-accent: #5b4a9c;

  --pastel-quiz-bg: #e3f5f4;
  --pastel-quiz-border: #bfe6e3;
  --pastel-quiz-accent: #16706c;

  /* Rendu des formules */
  --formula-bg: var(--pastel-formula-bg);
  --formula-border: var(--pastel-formula-border);
  --formula-text: #17202a;

  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

/* -------------------------------------------------------------------------
   2. PALETTE — MODE SOMBRE
   -------------------------------------------------------------------------
   Bleu nuit / ardoise. Les cartes sont volontairement plus claires que le
   fond, le texte est un blanc cassé, et les pastels sont désaturés plutôt
   qu'inversés. Aucun noir pur, aucun blanc pur.

   Le bloc est écrit deux fois, volontairement :
   - sous @media, pour le mode « Système » (aucun attribut posé) ;
   - sous [data-theme="dark"], pour le choix manuel de l'utilisateur.
   ------------------------------------------------------------------------- */

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    color-scheme: dark;

    --background: #0e1620;
    --background-glow: rgba(80, 150, 200, 0.1);
    --surface: #17222f;
    --surface-secondary: #1d2a38;
    --surface-raised: #22303f;

    --text-primary: #e9eef4;
    --text-secondary: #a2b2c3;
    --text-heading: #dce7f2;
    --text-on-accent: #08161f;

    --border: #2b3a4b;
    --border-strong: #3c4f64;
    --panel-border: rgba(150, 190, 220, 0.12);

    --accent: #7cc0e6;
    --accent-strong: #9ad2f2;
    --accent-soft: #17303f;
    --accent-glow: rgba(124, 192, 230, 0.22);

    --success: #74d3a0;
    --success-bg: #17302a;
    --success-border: #2b5344;
    --error: #f0908f;
    --error-bg: #331f21;
    --error-border: #57363a;
    --focus-ring: #f0c765;

    --selected-bg: #17364a;
    --selected-border: #6fb2d8;
    --selected-letter-text: #08161f;
    --letter-bg: #26364a;
    --letter-text: #cfe2f0;

    --header-bg: #101c28;
    --header-text: #eef3f8;
    --header-rule: #d4a944;
    --header-control-bg: rgba(255, 255, 255, 0.08);
    --header-control-border: rgba(255, 255, 255, 0.16);
    --header-control-hover: rgba(255, 255, 255, 0.16);
    --header-control-active-bg: #cfe2f0;
    --header-control-active-text: #101c28;

    --score-bg: #1d2c3c;
    --score-text: #eef3f8;
    --score-label: rgba(233, 238, 244, 0.7);

    --track-bg: #22303f;

    --disabled-bg: #232f3c;
    --disabled-text: #6d7d8d;

    --shadow: 0 18px 50px rgba(0, 0, 0, 0.45);
    --shadow-soft: 0 6px 16px rgba(0, 0, 0, 0.4);
    --shadow-card: 0 2px 10px rgba(0, 0, 0, 0.3);
    --shadow-card-hover: 0 12px 28px rgba(0, 0, 0, 0.45);

    --pastel-definition-bg: #16283a;
    --pastel-definition-border: #27435c;
    --pastel-definition-accent: #8ec8ea;

    --pastel-formula-bg: #302416;
    --pastel-formula-border: #4c3a23;
    --pastel-formula-accent: #e8b06a;

    --pastel-method-bg: #17302a;
    --pastel-method-border: #2b5344;
    --pastel-method-accent: #7fd6a5;

    --pastel-example-bg: #241f36;
    --pastel-example-border: #3a3352;
    --pastel-example-accent: #b3a5e6;

    --pastel-quiz-bg: #12302f;
    --pastel-quiz-border: #234745;
    --pastel-quiz-accent: #74cbc6;

    --formula-text: #f2ede6;
  }
}

:root[data-theme="dark"] {
  color-scheme: dark;

  --background: #0e1620;
  --background-glow: rgba(80, 150, 200, 0.1);
  --surface: #17222f;
  --surface-secondary: #1d2a38;
  --surface-raised: #22303f;

  --text-primary: #e9eef4;
  --text-secondary: #a2b2c3;
  --text-heading: #dce7f2;
  --text-on-accent: #08161f;

  --border: #2b3a4b;
  --border-strong: #3c4f64;
  --panel-border: rgba(150, 190, 220, 0.12);

  --accent: #7cc0e6;
  --accent-strong: #9ad2f2;
  --accent-soft: #17303f;
  --accent-glow: rgba(124, 192, 230, 0.22);

  --success: #74d3a0;
  --success-bg: #17302a;
  --success-border: #2b5344;
  --error: #f0908f;
  --error-bg: #331f21;
  --error-border: #57363a;
  --focus-ring: #f0c765;

  --selected-bg: #17364a;
  --selected-border: #6fb2d8;
  --selected-letter-text: #08161f;
  --letter-bg: #26364a;
  --letter-text: #cfe2f0;

  --header-bg: #101c28;
  --header-text: #eef3f8;
  --header-rule: #d4a944;
  --header-control-bg: rgba(255, 255, 255, 0.08);
  --header-control-border: rgba(255, 255, 255, 0.16);
  --header-control-hover: rgba(255, 255, 255, 0.16);
  --header-control-active-bg: #cfe2f0;
  --header-control-active-text: #101c28;

  --score-bg: #1d2c3c;
  --score-text: #eef3f8;
  --score-label: rgba(233, 238, 244, 0.7);

  --track-bg: #22303f;

  --disabled-bg: #232f3c;
  --disabled-text: #6d7d8d;

  --shadow: 0 18px 50px rgba(0, 0, 0, 0.45);
  --shadow-soft: 0 6px 16px rgba(0, 0, 0, 0.4);
  --shadow-card: 0 2px 10px rgba(0, 0, 0, 0.3);
  --shadow-card-hover: 0 12px 28px rgba(0, 0, 0, 0.45);

  --pastel-definition-bg: #16283a;
  --pastel-definition-border: #27435c;
  --pastel-definition-accent: #8ec8ea;

  --pastel-formula-bg: #302416;
  --pastel-formula-border: #4c3a23;
  --pastel-formula-accent: #e8b06a;

  --pastel-method-bg: #17302a;
  --pastel-method-border: #2b5344;
  --pastel-method-accent: #7fd6a5;

  --pastel-example-bg: #241f36;
  --pastel-example-border: #3a3352;
  --pastel-example-accent: #b3a5e6;

  --pastel-quiz-bg: #12302f;
  --pastel-quiz-border: #234745;
  --pastel-quiz-accent: #74cbc6;

  --formula-text: #f2ede6;
}

/* -------------------------------------------------------------------------
   3. BASE
   ------------------------------------------------------------------------- */

* {
  box-sizing: border-box;
}

html {
  background: var(--background);
}

body {
  min-width: 320px;
  min-height: 100vh;
  margin: 0;
  color: var(--text-primary);
  background:
    radial-gradient(circle at top right, var(--background-glow), transparent 32rem),
    var(--background);
}

button {
  font: inherit;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  overflow: hidden;
  white-space: nowrap;
  clip: rect(0 0 0 0);
  clip-path: inset(50%);
  border: 0;
}

/* -------------------------------------------------------------------------
   4. BANDEAU
   ------------------------------------------------------------------------- */

.site-header {
  color: var(--header-text);
  background: var(--header-bg);
  border-bottom: 4px solid var(--header-rule);
}

.header-content {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  width: min(100% - 2rem, 900px);
  min-height: 76px;
  margin: 0 auto;
}

.header-identity {
  display: flex;
  align-items: center;
  gap: 0.9rem;
  min-width: 0;
}

.subject-label {
  flex-shrink: 0;
  padding: 0.4rem 0.7rem;
  font-size: 0.78rem;
  font-weight: 750;
  letter-spacing: 0.07em;
  text-transform: uppercase;
  border: 1px solid var(--header-control-border);
  border-radius: 999px;
}

.site-title {
  font-size: 1.05rem;
  font-weight: 700;
}

/* -------------------------------------------------------------------------
   5. SÉLECTEUR D'APPARENCE (Système / Clair / Sombre)
   ------------------------------------------------------------------------- */

.theme-switch {
  display: flex;
  flex-shrink: 0;
  gap: 2px;
  padding: 3px;
  background: var(--header-control-bg);
  border: 1px solid var(--header-control-border);
  border-radius: 999px;
}

.theme-option {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 32px;
  padding: 0;
  color: var(--header-text);
  cursor: pointer;
  background: transparent;
  border: 0;
  border-radius: 999px;
  transition: background 150ms ease, color 150ms ease;
}

.theme-option svg {
  width: 18px;
  height: 18px;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.7;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.theme-option:hover {
  background: var(--header-control-hover);
}

/* L'option active est déduite de data-theme, posé sur <html> avant le
   premier affichage : la pastille est donc correcte dès le premier rendu,
   sans attendre le JavaScript et sans scintillement. */
:root:not([data-theme]) .theme-option[data-theme-choice="system"],
:root[data-theme="light"] .theme-option[data-theme-choice="light"],
:root[data-theme="dark"] .theme-option[data-theme-choice="dark"] {
  color: var(--header-control-active-text);
  background: var(--header-control-active-bg);
}

.theme-option:focus-visible {
  outline: 3px solid var(--focus-ring);
  outline-offset: 2px;
}

/* -------------------------------------------------------------------------
   6. STRUCTURE DE PAGE
   ------------------------------------------------------------------------- */

.app-shell {
  width: min(100% - 2rem, 760px);
  min-height: calc(100vh - 154px);
  margin: 0 auto;
  padding: clamp(2rem, 7vw, 4.5rem) 0;
  outline: none;
}

.panel {
  padding: clamp(1.4rem, 5vw, 3rem);
  background: var(--surface);
  border: 1px solid var(--panel-border);
  border-radius: 20px;
  box-shadow: var(--shadow);
}

.eyebrow {
  margin: 0 0 0.6rem;
  color: var(--accent);
  font-size: 0.8rem;
  font-weight: 800;
  letter-spacing: 0.09em;
  text-transform: uppercase;
}

h1,
h2 {
  margin-top: 0;
  color: var(--text-heading);
  line-height: 1.2;
}

h1 {
  margin-bottom: 1rem;
  font-size: clamp(2rem, 8vw, 3.25rem);
  letter-spacing: -0.035em;
}

h2 {
  margin-bottom: 1.5rem;
  font-size: clamp(1.4rem, 5vw, 2rem);
}

.lead {
  max-width: 60ch;
  margin: 0 0 1.75rem;
  color: var(--text-secondary);
  font-size: 1.06rem;
  line-height: 1.65;
}

/* -------------------------------------------------------------------------
   7. CARTES DE QCM
   ------------------------------------------------------------------------- */

.quiz-card {
  padding: 1.25rem;
  background: var(--surface-secondary);
  border: 1px solid var(--border);
  border-radius: 14px;
}

.quiz-card h2 {
  margin-bottom: 0.55rem;
  font-size: 1.25rem;
}

.quiz-card p {
  margin: 0 0 1.25rem;
  color: var(--text-secondary);
  line-height: 1.5;
}

.quiz-meta {
  display: flex;
  gap: 1rem;
  margin-bottom: 1.25rem;
  color: var(--accent);
  font-size: 0.9rem;
  font-weight: 700;
}

/* -------------------------------------------------------------------------
   8. BOUTONS
   ------------------------------------------------------------------------- */

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 50px;
  padding: 0.75rem 1.25rem;
  color: var(--text-on-accent);
  font-weight: 750;
  text-align: center;
  cursor: pointer;
  background: var(--accent);
  border: 0;
  border-radius: 10px;
  transition: background 160ms ease, transform 160ms ease, box-shadow 160ms ease;
}

.button:hover:not(:disabled) {
  background: var(--accent-strong);
  box-shadow: var(--shadow-soft);
  transform: translateY(-1px);
}

.button:focus-visible,
.answer-option:focus-visible {
  outline: 3px solid var(--focus-ring);
  outline-offset: 3px;
}

.button:disabled {
  color: var(--disabled-text);
  cursor: not-allowed;
  background: var(--disabled-bg);
}

.button-wide {
  width: 100%;
}

/* -------------------------------------------------------------------------
   9. PROGRESSION
   ------------------------------------------------------------------------- */

.progress-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  margin-bottom: 0.75rem;
  color: var(--text-secondary);
  font-size: 0.9rem;
  font-weight: 700;
}

.progress-track {
  height: 8px;
  margin-bottom: 2rem;
  overflow: hidden;
  background: var(--track-bg);
  border-radius: 999px;
}

.progress-bar {
  height: 100%;
  background: var(--accent);
  border-radius: inherit;
  transition: width 220ms ease;
}

/* -------------------------------------------------------------------------
   10. QUESTION ET RÉPONSES
   ------------------------------------------------------------------------- */

.question-text {
  margin-bottom: 1.5rem;
  font-size: clamp(1.25rem, 4vw, 1.65rem);
}

.answers {
  display: grid;
  gap: 0.75rem;
  margin: 0 0 1.75rem;
  padding: 0;
  border: 0;
}

.answer-option {
  display: grid;
  grid-template-columns: 2.5rem 1fr;
  align-items: center;
  width: 100%;
  min-height: 60px;
  padding: 0.7rem 1rem;
  color: var(--text-primary);
  text-align: left;
  cursor: pointer;
  background: var(--surface);
  border: 2px solid var(--border);
  border-radius: 12px;
  transition: border-color 140ms ease, background 140ms ease;
}

.answer-option:hover {
  background: var(--surface-raised);
  border-color: var(--border-strong);
}

.answer-option[aria-checked="true"] {
  background: var(--selected-bg);
  border-color: var(--selected-border);
}

.answer-option[aria-checked="true"]:hover {
  background: var(--selected-bg);
}

.answer-letter {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 2rem;
  height: 2rem;
  color: var(--letter-text);
  font-weight: 800;
  background: var(--letter-bg);
  border-radius: 50%;
}

.answer-option[aria-checked="true"] .answer-letter {
  color: var(--selected-letter-text);
  background: var(--selected-border);
}

.answer-text {
  padding-left: 0.65rem;
  line-height: 1.4;
}

/* -------------------------------------------------------------------------
   11. RÉSULTATS
   ------------------------------------------------------------------------- */

.results-list {
  display: grid;
  gap: 0.65rem;
  margin: 1.5rem 0;
  padding: 0;
  list-style: none;
}

.result-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 0.9rem 1rem;
  font-weight: 700;
  border: 1px solid transparent;
  border-radius: 10px;
}

.result-correct {
  color: var(--success);
  background: var(--success-bg);
  border-color: var(--success-border);
}

.result-wrong {
  color: var(--error);
  background: var(--error-bg);
  border-color: var(--error-border);
}

.score-box {
  margin: 1.5rem 0;
  padding: 1.3rem;
  text-align: center;
  background: var(--score-bg);
  border-radius: 14px;
}

.score-label {
  display: block;
  margin-bottom: 0.3rem;
  color: var(--score-label);
  font-size: 0.88rem;
  font-weight: 700;
  text-transform: uppercase;
}

.score-value {
  color: var(--score-text);
  font-size: 2.3rem;
  font-weight: 850;
}

.retry-note,
.completion-note {
  margin: 1.25rem 0;
  color: var(--text-secondary);
  line-height: 1.55;
}

.corrections {
  margin-top: 2rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
}

.corrections h2 {
  margin-bottom: 1rem;
  font-size: 1.3rem;
}

.correction-list {
  display: grid;
  gap: 1rem;
  margin: 0;
  padding: 0;
  list-style: none;
}

.correction-item {
  padding: 1rem;
  background: var(--surface-secondary);
  border-left: 4px solid var(--accent);
  border-radius: 8px;
}

.correction-question {
  display: block;
  margin-bottom: 0.4rem;
  color: var(--text-heading);
  line-height: 1.45;
}

.correction-answer {
  color: var(--success);
  font-weight: 750;
  line-height: 1.45;
}

/* -------------------------------------------------------------------------
   12. CHARGEMENT ET ERREUR
   ------------------------------------------------------------------------- */

.error-panel {
  text-align: center;
}

.error-panel p,
.loading-panel {
  color: var(--text-secondary);
  line-height: 1.6;
}

.site-footer {
  width: min(100% - 2rem, 900px);
  min-height: 78px;
  margin: 0 auto;
  color: var(--text-secondary);
  font-size: 0.82rem;
  text-align: center;
}

/* -------------------------------------------------------------------------
   13. BLOCS DE COURS ET FORMULES (préparation du Chapitre 1)
   ------------------------------------------------------------------------- */

.course-block {
  margin: 0 0 1.25rem;
  padding: 1.1rem 1.25rem;
  background: var(--surface-secondary);
  border: 1px solid var(--border);
  border-left: 4px solid var(--accent);
  border-radius: 12px;
  line-height: 1.6;
}

.course-block-definition {
  background: var(--pastel-definition-bg);
  border-color: var(--pastel-definition-border);
  border-left-color: var(--pastel-definition-accent);
}

.course-block-formula {
  background: var(--pastel-formula-bg);
  border-color: var(--pastel-formula-border);
  border-left-color: var(--pastel-formula-accent);
}

.course-block-method {
  background: var(--pastel-method-bg);
  border-color: var(--pastel-method-border);
  border-left-color: var(--pastel-method-accent);
}

.course-block-example {
  background: var(--pastel-example-bg);
  border-color: var(--pastel-example-border);
  border-left-color: var(--pastel-example-accent);
}

.course-block-quiz {
  background: var(--pastel-quiz-bg);
  border-color: var(--pastel-quiz-border);
  border-left-color: var(--pastel-quiz-accent);
}

.course-block-title {
  display: block;
  margin-bottom: 0.5rem;
  font-size: 0.78rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.course-block-definition .course-block-title {
  color: var(--pastel-definition-accent);
}

.course-block-formula .course-block-title {
  color: var(--pastel-formula-accent);
}

.course-block-method .course-block-title {
  color: var(--pastel-method-accent);
}

.course-block-example .course-block-title {
  color: var(--pastel-example-accent);
}

.course-block-quiz .course-block-title {
  color: var(--pastel-quiz-accent);
}

/* Formule mise en évidence, en attendant le moteur de rendu mathématique.
   Les couleurs suivent déjà le thème, quel que soit le rendu retenu. */
.formula {
  display: block;
  margin: 0.75rem 0;
  padding: 0.85rem 1rem;
  overflow-x: auto;
  color: var(--formula-text);
  font-size: 1.15rem;
  text-align: center;
  background: var(--formula-bg);
  border: 1px solid var(--formula-border);
  border-radius: 10px;
}

.formula-inline {
  padding: 0.1rem 0.35rem;
  color: var(--formula-text);
  background: var(--formula-bg);
  border: 1px solid var(--formula-border);
  border-radius: 5px;
  white-space: nowrap;
}

/* -------------------------------------------------------------------------
   14. RESPONSIVE
   ------------------------------------------------------------------------- */

@media (max-width: 560px) {
  .header-content {
    min-height: 66px;
    padding: 0.6rem 0;
  }

  .header-identity {
    flex-direction: column;
    align-items: flex-start;
    gap: 0.35rem;
  }

  .subject-label {
    padding: 0.25rem 0.55rem;
    font-size: 0.68rem;
  }

  .site-title {
    font-size: 0.95rem;
  }

  .theme-option {
    width: 38px;
    height: 34px;
  }

  .app-shell {
    width: min(100% - 1rem, 760px);
    min-height: calc(100vh - 136px);
    padding: 1rem 0 2rem;
  }

  .panel {
    border-radius: 15px;
  }

  .result-item {
    align-items: flex-start;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    transition-duration: 0.01ms !important;
  }
}

/* =========================================================================
   15. CATALOGUE DES CHAPITRES ET PAGES DE CHAPITRE
   -------------------------------------------------------------------------
   Écrans repris de l'application iOS : très aérés, cartes arrondies,
   numéros dans des blocs bleus, organisation par partie et sous-partie.
   Toutes les couleurs viennent des variables Clair / Sombre.
   ========================================================================= */

.app-shell-wide {
  width: min(100% - 2rem, 1060px);
}

/* --- Barre de navigation contextuelle --- */

.page-nav {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  gap: 1rem;
  margin-bottom: clamp(1.75rem, 5vw, 3rem);
  padding-bottom: 1rem;
  border-bottom: 1px solid var(--border);
}

.nav-back {
  display: inline-flex;
  align-items: center;
  gap: 0.15rem;
  justify-self: start;
  min-height: 44px;
  padding: 0.35rem 0.7rem 0.35rem 0.35rem;
  color: var(--accent);
  font-weight: 700;
  text-decoration: none;
  border-radius: 10px;
}

.nav-back:hover {
  background: var(--accent-soft);
}

.nav-back:focus-visible {
  outline: 3px solid var(--focus-ring);
  outline-offset: 2px;
}

.nav-back svg {
  width: 20px;
  height: 20px;
  fill: none;
  stroke: currentColor;
  stroke-width: 2.2;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.nav-title {
  color: var(--text-secondary);
  font-size: 0.95rem;
  font-weight: 750;
  text-align: center;
}

.nav-side {
  justify-self: end;
}

/* --- En-tête d'écran --- */

.hero {
  margin-bottom: clamp(2rem, 6vw, 3.5rem);
}

.hero h1 {
  margin-bottom: 0.75rem;
  font-size: clamp(2rem, 6vw, 3rem);
}

.hero .lead {
  margin-bottom: 1rem;
}

.official-label {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  margin: 0;
  padding: 0.4rem 0.85rem;
  color: var(--accent);
  font-size: 0.85rem;
  font-weight: 750;
  background: var(--accent-soft);
  border-radius: 999px;
}

.official-label svg {
  width: 17px;
  height: 17px;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.8;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.dev-note {
  margin: 1rem 0 0;
  color: var(--text-secondary);
  font-size: 0.85rem;
}

/* --- Parties et sous-parties --- */

.parts {
  display: grid;
  gap: clamp(2.5rem, 7vw, 4rem);
}

.part-header {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin-bottom: 1.75rem;
}

.part-number {
  display: inline-flex;
  flex-shrink: 0;
  align-items: center;
  justify-content: center;
  width: 46px;
  height: 46px;
  color: var(--text-on-accent);
  font-size: 1.3rem;
  font-weight: 800;
  background: var(--accent);
  border-radius: 14px;
}

.part-copy {
  display: block;
  min-width: 0;
}

.part-label {
  display: block;
  margin-bottom: 0.15rem;
  color: var(--accent);
  font-size: 0.76rem;
  font-weight: 800;
  letter-spacing: 0.09em;
  text-transform: uppercase;
}

.part-title {
  margin: 0;
  font-size: clamp(1.15rem, 3vw, 1.45rem);
  line-height: 1.3;
}

.groups {
  display: grid;
  gap: 2.25rem;
}

.group-title {
  display: flex;
  align-items: center;
  gap: 0.65rem;
  margin: 0 0 1rem;
  color: var(--text-secondary);
  font-size: 0.95rem;
  font-weight: 750;
  line-height: 1.4;
}

.group-letter {
  display: inline-flex;
  flex-shrink: 0;
  align-items: center;
  justify-content: center;
  width: 26px;
  height: 26px;
  color: var(--accent);
  font-size: 0.85rem;
  font-weight: 800;
  background: var(--accent-soft);
  border-radius: 8px;
}

/* --- Carte de chapitre --- */

.chapter-grid,
.section-grid {
  display: grid;
  gap: 1rem;
}

.chapter-card {
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: 1.1rem;
  padding: 1.15rem 1.25rem;
  color: inherit;
  text-decoration: none;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 18px;
  box-shadow: var(--shadow-card);
  transition: border-color 150ms ease, transform 150ms ease, box-shadow 150ms ease;
}

.chapter-card:hover {
  border-color: var(--accent);
  box-shadow: var(--shadow-card-hover);
  transform: translateY(-2px);
}

.chapter-card:focus-visible {
  outline: 3px solid var(--focus-ring);
  outline-offset: 3px;
}

.chapter-number {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 52px;
  height: 52px;
  color: var(--text-on-accent);
  font-size: 1.15rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  background: var(--accent);
  border-radius: 15px;
}

.chapter-copy {
  display: block;
  min-width: 0;
}

.chapter-label {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  margin-bottom: 0.2rem;
  color: var(--text-secondary);
  font-size: 0.76rem;
  font-weight: 800;
  letter-spacing: 0.07em;
  text-transform: uppercase;
}

.chapter-tag {
  padding: 0.1rem 0.45rem;
  color: var(--text-secondary);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.03em;
  text-transform: none;
  background: var(--surface-raised);
  border: 1px solid var(--border);
  border-radius: 999px;
}

.chapter-title {
  display: block;
  margin-bottom: 0.25rem;
  color: var(--text-heading);
  font-size: 1.1rem;
  font-weight: 750;
  line-height: 1.3;
}

.chapter-description {
  display: block;
  color: var(--text-secondary);
  font-size: 0.92rem;
  line-height: 1.45;
}

.chapter-chevron {
  display: inline-flex;
  color: var(--text-secondary);
}

.chapter-chevron svg {
  width: 22px;
  height: 22px;
  fill: none;
  stroke: currentColor;
  stroke-width: 2.1;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.chapter-card:hover .chapter-chevron {
  color: var(--accent);
}

/* Réservé au futur mode élève : aucun chapitre n'utilise cet état
   en mode développement. */
.chapter-card-locked {
  opacity: 0.55;
}

/* --- Rubriques d'un chapitre --- */

.section-card {
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: 1.1rem;
  padding: 1.3rem 1.35rem;
  color: inherit;
  text-decoration: none;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 18px;
  box-shadow: var(--shadow-card);
  transition: border-color 150ms ease, transform 150ms ease, box-shadow 150ms ease;
}

.section-card:hover {
  box-shadow: var(--shadow-card-hover);
  transform: translateY(-2px);
}

.section-card:focus-visible {
  outline: 3px solid var(--focus-ring);
  outline-offset: 3px;
}

.section-icon {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 50px;
  height: 50px;
  border-radius: 15px;
}

.section-icon svg {
  width: 24px;
  height: 24px;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.8;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.section-title {
  display: block;
  margin-bottom: 0.2rem;
  color: var(--text-heading);
  font-size: 1.12rem;
  font-weight: 750;
}

.section-description {
  display: block;
  color: var(--text-secondary);
  font-size: 0.92rem;
  line-height: 1.45;
}

.section-card-definition .section-icon {
  color: var(--pastel-definition-accent);
  background: var(--pastel-definition-bg);
}

.section-card-definition:hover {
  border-color: var(--pastel-definition-accent);
}

.section-card-formula .section-icon {
  color: var(--pastel-formula-accent);
  background: var(--pastel-formula-bg);
}

.section-card-formula:hover {
  border-color: var(--pastel-formula-accent);
}

.section-card-example .section-icon {
  color: var(--pastel-example-accent);
  background: var(--pastel-example-bg);
}

.section-card-example:hover {
  border-color: var(--pastel-example-accent);
}

/* --- Page « Contenu en préparation » --- */

.placeholder-panel {
  text-align: center;
}

.placeholder-icon {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 62px;
  height: 62px;
  margin-bottom: 1.25rem;
  color: var(--accent);
  background: var(--accent-soft);
  border-radius: 20px;
}

.placeholder-icon svg {
  width: 28px;
  height: 28px;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.7;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.placeholder-panel .lead {
  margin-inline: auto;
}

a.button {
  text-decoration: none;
}

/* --- Liens de pied de page --- */

.footer-links {
  display: flex;
  gap: 0.5rem;
  justify-content: center;
  margin: 0.35rem 0 0;
}

.footer-links a {
  color: var(--text-secondary);
}

.footer-links a:hover {
  color: var(--accent);
}

/* --- Adaptation à la largeur --- */

@media (min-width: 900px) {
  .chapter-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 1.15rem;
  }

  .section-grid {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }

  .section-card {
    grid-template-columns: 1fr;
    align-items: start;
    gap: 0.9rem;
    padding: 1.6rem;
  }

  .section-card .chapter-chevron {
    display: none;
  }
}

@media (max-width: 560px) {
  .page-nav {
    margin-bottom: 1.5rem;
  }

  .chapter-card,
  .section-card {
    gap: 0.9rem;
    padding: 1rem;
    border-radius: 16px;
  }

  .chapter-number {
    width: 46px;
    height: 46px;
    font-size: 1.05rem;
    border-radius: 13px;
  }

  .chapter-title {
    font-size: 1.02rem;
  }

  .part-number {
    width: 40px;
    height: 40px;
    font-size: 1.15rem;
  }
}

/* =========================================================================
   16. SOMMAIRE DU COURS D'UN CHAPITRE
   ========================================================================= */

.chapter-kicker {
  margin: 0 0 0.4rem;
  color: var(--text-secondary);
  font-size: 0.82rem;
  font-weight: 800;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.course-outline {
  display: grid;
  gap: 0.8rem;
  margin: 0;
  padding: 0;
  list-style: none;
  counter-reset: none;
}

.course-step {
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: 1.1rem;
  padding: 1.05rem 1.25rem;
  color: inherit;
  text-decoration: none;
  background: var(--surface);
  border: 1px solid var(--border);
  border-left: 4px solid var(--accent);
  border-radius: 16px;
  box-shadow: var(--shadow-card);
  transition: border-color 150ms ease, transform 150ms ease, box-shadow 150ms ease;
}

.course-step:hover {
  box-shadow: var(--shadow-card-hover);
  transform: translateX(3px);
}

.course-step:focus-visible {
  outline: 3px solid var(--focus-ring);
  outline-offset: 3px;
}

.course-step-number {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 44px;
  height: 44px;
  font-size: 1.05rem;
  font-weight: 800;
  border-radius: 50%;
}

.course-step-title {
  display: block;
  margin-bottom: 0.15rem;
  color: var(--text-heading);
  font-size: 1.05rem;
  font-weight: 750;
  line-height: 1.35;
}

.course-step-subtitle {
  display: block;
  color: var(--text-secondary);
  font-size: 0.92rem;
  line-height: 1.45;
}

/* Tons repris des couleurs sémantiques du cours :
   bleu pour les notions, orange pour le formulaire, lavande pour
   l'entraînement final. */
.course-step-definition {
  border-left-color: var(--pastel-definition-accent);
}

.course-step-definition .course-step-number {
  color: var(--pastel-definition-accent);
  background: var(--pastel-definition-bg);
}

.course-step-definition:hover {
  border-color: var(--pastel-definition-accent);
}

.course-step-formula {
  border-left-color: var(--pastel-formula-accent);
}

.course-step-formula .course-step-number {
  color: var(--pastel-formula-accent);
  background: var(--pastel-formula-bg);
}

.course-step-formula:hover {
  border-color: var(--pastel-formula-accent);
}

.course-step-example {
  border-left-color: var(--pastel-example-accent);
}

.course-step-example .course-step-number {
  color: var(--pastel-example-accent);
  background: var(--pastel-example-bg);
}

.course-step-example:hover {
  border-color: var(--pastel-example-accent);
}

/* Lecture verticale conservée sur grand écran : la colonne du sommaire
   reste confortable au lieu de s'étirer sur toute la largeur. */
@media (min-width: 900px) {
  .course-outline {
    max-width: 820px;
  }
}

@media (max-width: 560px) {
  .course-step {
    gap: 0.85rem;
    padding: 0.95rem 1rem;
    border-radius: 14px;
  }

  .course-step-number {
    width: 38px;
    height: 38px;
    font-size: 0.95rem;
  }

  .course-step-title {
    font-size: 1rem;
  }
}

/* =========================================================================
   17. CONTENU D'UNE SOUS-PARTIE DE COURS
   ========================================================================= */

.course-body {
  display: grid;
  gap: 1.5rem;
  margin-bottom: 3rem;
}

.course-block {
  margin: 0;
  padding: clamp(1.25rem, 3vw, 1.9rem);
  border-radius: 18px;
}

.course-block p {
  margin: 0 0 0.85rem;
  line-height: 1.65;
}

.course-block p:last-child {
  margin-bottom: 0;
}

.course-block-heading {
  margin: 0 0 1rem;
  font-size: clamp(1.2rem, 3vw, 1.5rem);
}

/* --- Le saviez-vous ? --- */

.curiosity {
  margin-top: 1.25rem;
  padding: 1rem 1.15rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 14px;
}

.curiosity-eyebrow {
  margin: 0 0 0.4rem !important;
  color: var(--pastel-example-accent);
  font-size: 0.75rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.curiosity-value {
  margin-top: 0.6rem !important;
  font-weight: 750;
  text-align: center;
}

/* --- Audio --- */

.audio-block {
  display: grid;
  gap: 0.5rem;
  margin: 0 0 1.25rem;
  padding: 0.9rem 1rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 14px;
}

.audio-block figcaption {
  display: grid;
  gap: 0.1rem;
  font-size: 0.9rem;
}

.audio-block figcaption span {
  color: var(--text-secondary);
  font-size: 0.82rem;
}

.audio-block audio {
  width: 100%;
}

/* --- Formules --- */

.formula-grid {
  display: grid;
  gap: 1rem;
}

.formula-card {
  display: grid;
  gap: 0.7rem;
  justify-items: center;
  padding: 1.1rem;
  background: var(--surface);
  border: 1px solid var(--formula-border);
  border-radius: 14px;
}

.formula-label {
  color: var(--pastel-formula-accent);
  font-size: 0.72rem;
  font-weight: 800;
  letter-spacing: 0.07em;
  text-align: center;
  text-transform: uppercase;
}

.formula-line {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  color: var(--formula-text);
  font-size: 1.3rem;
  line-height: 1.2;
}

.formula-left,
.formula-result {
  font-weight: 750;
}

.formula-equals {
  color: var(--text-secondary);
}

.frac {
  display: inline-grid;
  /* Les deux lignes occupent la largeur de la plus large : la barre de
     fraction couvre donc tout le numérateur, même long. */
  justify-items: stretch;
  text-align: center;
  vertical-align: middle;
}

.frac-num,
.frac-den {
  white-space: nowrap;
}

.frac-num {
  padding: 0 0.35rem 0.15rem;
}

.frac-den {
  padding: 0.15rem 0.35rem 0;
  border-top: 2px solid currentColor;
}

/* --- Méthode et exemple guidé --- */

.method-steps {
  display: grid;
  gap: 0.9rem;
  margin: 0;
  padding: 0;
  list-style: none;
  counter-reset: none;
}

.method-step {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 0.9rem;
  align-items: start;
  line-height: 1.6;
}

.method-step-number {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  color: var(--text-on-accent);
  font-size: 0.9rem;
  font-weight: 800;
  background: var(--accent);
  border-radius: 50%;
}

.method-step-body {
  display: grid;
  gap: 0.6rem;
}

.method-step .formula {
  margin: 0;
  overflow-x: auto;
  text-align: left;
}

.example-prompt {
  margin-bottom: 1.5rem;
  padding: 1.1rem 1.25rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 14px;
}

.example-value {
  margin: 0.4rem 0 !important;
  font-size: 1.15rem;
  font-weight: 750;
  text-align: center;
}

.example-question {
  margin-bottom: 0 !important;
  color: var(--text-secondary);
}

/* Sur grand écran, la méthode en 3 réflexes se lit en trois colonnes. */
@media (min-width: 900px) {
  .formula-grid {
    grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  }

  .method-steps-example {
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 1.5rem;
  }

  .method-steps-example .method-step {
    grid-template-columns: 1fr;
    align-content: start;
    gap: 0.8rem;
    padding: 1.1rem;
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: 14px;
  }
}

/* =========================================================================
   18. VÉRIFIER CE QUE J'AI COMPRIS
   ========================================================================= */

.course-check {
  padding: clamp(1.4rem, 4vw, 2.25rem);
  background: var(--pastel-quiz-bg);
  border: 1px solid var(--pastel-quiz-border);
  border-radius: 20px;
}

.course-check-title {
  margin-bottom: 0.4rem;
  font-size: clamp(1.3rem, 3.5vw, 1.7rem);
}

.course-check-intro {
  margin: 0 0 1.25rem;
  color: var(--text-secondary);
}

.check-head {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 0.75rem;
}

.check-skill {
  color: var(--pastel-quiz-accent);
  font-size: 0.76rem;
  font-weight: 800;
  letter-spacing: 0.07em;
  text-transform: uppercase;
}

.check-progress {
  color: var(--text-secondary);
  font-size: 0.9rem;
  font-weight: 750;
}

.check-prompt {
  margin: 1.25rem 0 1.25rem;
  font-size: clamp(1.05rem, 2.5vw, 1.25rem);
  line-height: 1.55;
}

.check-options {
  display: grid;
  gap: 0.7rem;
  margin-bottom: 1.25rem;
}

.check-option {
  min-height: 54px;
  padding: 0.8rem 1.1rem;
  color: var(--text-primary);
  text-align: left;
  cursor: pointer;
  background: var(--surface);
  border: 2px solid var(--border);
  border-radius: 12px;
  transition: border-color 140ms ease, background 140ms ease;
}

.check-option:hover:not(:disabled) {
  border-color: var(--border-strong);
}

.check-option[aria-checked="true"] {
  background: var(--selected-bg);
  border-color: var(--selected-border);
}

.check-option:disabled {
  cursor: default;
  opacity: 0.75;
}

.check-option:focus-visible {
  outline: 3px solid var(--focus-ring);
  outline-offset: 3px;
}

.check-correct-answer {
  font-weight: 750;
}

.check-correction-steps {
  margin: 0 0 0.6rem;
  padding-left: 1.25rem;
  line-height: 1.6;
}

.check-common-errors {
  color: var(--text-secondary);
}

.course-check .progress-track {
  margin-bottom: 0;
}

/* =========================================================================
   19. BLOCS PROPRES AU PARAGRAPHE 2 (MASSE MOLAIRE)
   -------------------------------------------------------------------------
   Mêmes cartes, mêmes couleurs sémantiques et mêmes espacements que le
   paragraphe 1 : seuls les gabarits nouveaux de la source sont ajoutés.
   ========================================================================= */

/* --- Case du tableau périodique --- */

.atom-card {
  display: grid;
  gap: 0.6rem;
  justify-items: center;
  margin: 1.25rem 0 0;
}

/* Positions reprises telles quelles de la vue iOS
   (CourseAtomicMolarMassExampleCard) : carte de 112 × 148 points, chaque
   élément centré sur son point d'ancrage.
       nombre de nucléons  (19, 20)
       symbole             (56, 53)
       numéro atomique     (17, 78)
       nom                 (56, 105)
       masse molaire       (56, 127)
   Les valeurs CSS retirent les 2 px de bordure, car le positionnement
   absolu part du bord intérieur de la carte.                            */
.atom-tile {
  position: relative;
  width: 112px;
  height: 148px;
  background: var(--surface);
  border: 2px solid var(--pastel-definition-accent);
  border-radius: 17px;
}

.atom-tile > span {
  position: absolute;
  transform: translate(-50%, -50%);
  white-space: nowrap;
}

.atom-nucleons {
  top: 18px;   /* 20 − 2 */
  left: 17px;  /* 19 − 2 */
  font-size: 15px;
}

.atom-symbol {
  top: 51px;   /* 53 − 2 */
  left: 54px;  /* 56 − 2, centre de la carte */
  color: var(--pastel-definition-accent);
  font-size: 43px;
  font-weight: 800;
  line-height: 1;
}

.atom-protons {
  top: 76px;   /* 78 − 2 */
  left: 15px;  /* 17 − 2 */
  font-size: 15px;
}

.atom-nucleons,
.atom-protons {
  color: var(--text-secondary);
  font-weight: 750;
}

.atom-name {
  top: 103px;  /* 105 − 2 */
  left: 54px;
  color: var(--text-secondary);
  font-size: 15px;
}

.atom-mass {
  top: 125px;  /* 127 − 2 */
  left: 54px;
  font-size: 17px;
  font-weight: 750;
}

.atom-card figcaption {
  color: var(--text-secondary);
  font-size: 0.85rem;
  text-align: center;
}

/* --- Étapes courtes : compter, multiplier, additionner --- */

.summary-chips {
  display: flex;
  flex-wrap: wrap;
  gap: 0.6rem;
  margin: 1.25rem 0;
  padding: 0;
  list-style: none;
}

.summary-chip {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.45rem 0.9rem 0.45rem 0.45rem;
  font-weight: 750;
  background: var(--surface);
  border: 1px solid var(--formula-border);
  border-radius: 999px;
}

.summary-chip-number {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 26px;
  height: 26px;
  color: var(--text-on-accent);
  font-size: 0.82rem;
  font-weight: 800;
  background: var(--pastel-formula-accent);
  border-radius: 50%;
}

/* --- Exemples : molécule et ion polyatomique --- */

.molar-examples {
  display: grid;
  gap: 1rem;
  margin-top: 1.25rem;
}

.molar-example {
  padding: 1.15rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 14px;
}

.molar-example-badge {
  display: inline-block;
  margin-bottom: 0.5rem;
  padding: 0.2rem 0.6rem;
  font-size: 0.68rem;
  font-weight: 800;
  letter-spacing: 0.07em;
  border-radius: 999px;
}

.molar-example-molecule .molar-example-badge {
  color: var(--pastel-definition-accent);
  background: var(--pastel-definition-bg);
}

.molar-example-polyatomicIon .molar-example-badge {
  color: var(--pastel-example-accent);
  background: var(--pastel-example-bg);
}

.molar-example-title {
  margin: 0 0 0.3rem;
  font-size: 1.05rem;
}

.molar-example-count {
  margin: 0 0 0.6rem !important;
  color: var(--text-secondary);
  font-weight: 750;
}

.molar-example-note {
  color: var(--text-secondary);
  font-size: 0.9rem;
}

.molar-example .formula {
  margin: 0.6rem 0;
  font-size: 1.05rem;
}

.molar-example-result {
  margin: 0 !important;
  font-size: 1.15rem;
  font-weight: 800;
  text-align: center;
}

/* --- Méthode en cartes numérotées --- */

.method-steps-cards .method-step {
  padding: 1rem 1.1rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 14px;
}

.method-steps-cards .method-step-number {
  background: var(--pastel-method-accent);
}

/* --- Exemple guidé de la section 2 --- */

.guided-step-title {
  color: var(--text-heading);
}

.guided-result {
  margin: 1.5rem 0 0 !important;
  padding: 0.9rem 1rem;
  font-size: 1.2rem;
  font-weight: 800;
  text-align: center;
  background: var(--surface);
  border: 1px solid var(--pastel-example-border);
  border-radius: 14px;
}

@media (min-width: 900px) {
  .molar-examples {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .method-steps-cards {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

/* =========================================================================
   20. AJOUTS DU PARAGRAPHE 3 (MASSE ET QUANTITÉ)
   ========================================================================= */

/* Forme équivalente d'une relation, telle que fournie par la source. */
.formula-equivalent {
  display: block;
  margin-top: 0.35rem;
  color: var(--text-secondary);
  text-align: center;
}

.formula-equivalent .formula-line {
  font-size: 1.05rem;
}

/* Étapes de calcul sans numéro : la lecture suit la suite des égalités. */
.method-steps-plain {
  gap: 0.6rem;
}

.method-steps-plain .method-step {
  grid-template-columns: 1fr;
}

.method-steps-plain .formula {
  margin: 0;
}

/* =========================================================================
   21. DÉROULÉ DU QUESTIONNAIRE DE COURS
   -------------------------------------------------------------------------
   Navigation entre les questions, score de tentative, puis corrigé final.
   ========================================================================= */

.check-nav {
  display: flex;
  gap: 0.75rem;
}

.check-nav .button {
  flex: 1;
}

.button-secondary {
  color: var(--accent);
  background: var(--surface);
  border: 1px solid var(--border-strong);
}

.button-secondary:hover:not(:disabled) {
  color: var(--accent);
  background: var(--accent-soft);
}

.button-secondary:disabled {
  color: var(--disabled-text);
  background: var(--disabled-bg);
  border-color: transparent;
}

.check-retry-note {
  margin: 0.9rem 0 0;
  color: var(--text-secondary);
  font-size: 0.92rem;
  line-height: 1.55;
}

.check-retry-note {
  margin-bottom: 1.25rem;
  text-align: center;
}

.score-percentage {
  display: block;
  margin-top: 0.2rem;
  color: var(--score-label);
  font-size: 1.1rem;
  font-weight: 750;
}

/* --- Corrigé, affiché seulement à la toute fin --- */

.check-corrections {
  margin-top: 2rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
}

.check-corrections-title {
  margin: 0 0 1rem;
  color: var(--text-heading);
  font-size: 1.25rem;
}

.check-corrections-list {
  display: grid;
  gap: 1rem;
  margin: 0;
  padding: 0;
  list-style: none;
}

.check-correction {
  padding: 1.1rem 1.25rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 14px;
  line-height: 1.6;
}

.check-correction p {
  margin: 0 0 0.6rem;
}

.check-correction p:last-child {
  margin-bottom: 0;
}

.check-correction-head {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 0.6rem;
}

.check-correction-index {
  color: var(--text-secondary);
  font-size: 0.76rem;
  font-weight: 800;
  letter-spacing: 0.07em;
  text-transform: uppercase;
}

.check-correction-status {
  padding: 0.2rem 0.6rem;
  font-size: 0.8rem;
  font-weight: 750;
  border-radius: 999px;
}

.check-correction-prompt {
  font-weight: 700;
}

/* =========================================================================
   22. AJOUT DU PARAGRAPHE 4 (LIQUIDES)
   ========================================================================= */

/* Remarques sous les relations : origine d'une formule, valeur de ρₑₐᵤ… */
.formula-notes {
  display: grid;
  gap: 0.5rem;
  margin: 1.25rem 0 0;
  padding-left: 1.15rem;
  color: var(--text-secondary);
  line-height: 1.6;
}

/* Indices scientifiques rendus par <sub> : compacts, sans décalage
   entre les lettres et sans perturber l'interligne. */
sub {
  font-size: 0.68em;
  line-height: 0;
  letter-spacing: 0;
  vertical-align: -0.22em;
}

/* =========================================================================
   23. PARAGRAPHE 6 — BLOC « RELATIONS UTILES »
   -------------------------------------------------------------------------
   Ce bloc contient des membres de gauche écrits en toutes lettres
   (« proportion de A », « pourcentage de A ») : sans réduction, les
   expressions se coupent dans des cartes en trois colonnes.
   La règle est limitée à ce seul bloc, par son identifiant source.
   ========================================================================= */

[data-block="melange-formules"] .formula-card {
  padding: 0.95rem 0.8rem;
}

[data-block="melange-formules"] .formula-line {
  gap: 0.35rem;
  font-size: clamp(0.78rem, 1.05vw, 0.95rem);
}

[data-block="melange-formules"] .formula-left,
[data-block="melange-formules"] .frac-linear,
[data-block="melange-formules"] .frac-num,
[data-block="melange-formules"] .frac-den {
  white-space: nowrap;
}

@media (max-width: 899px) {
  [data-block="melange-formules"] .formula-line {
    font-size: clamp(0.9rem, 3.4vw, 1.15rem);
  }
}

/* Deux relations sur la première ligne, la troisième seule en dessous et
   pleine largeur : elle est la plus longue des trois.
   Sous 900 px, la grille reste à une colonne : les cartes s'empilent. */
@media (min-width: 900px) {
  [data-block="melange-formules"] .formula-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  [data-block="melange-formules"] .formula-card:nth-child(3) {
    grid-column: 1 / -1;
  }
}

/* =========================================================================
   24. PARAGRAPHE 7 — FORMULAIRE
   -------------------------------------------------------------------------
   Cinq relations : trois sur la première ligne, deux sur la seconde,
   sans espace vide en bout de ligne. Limité à ce bloc.
   ========================================================================= */

@media (min-width: 900px) {
  [data-block="formulaire-relations"] .formula-grid {
    grid-template-columns: repeat(6, minmax(0, 1fr));
  }

  [data-block="formulaire-relations"] .formula-card {
    grid-column: span 2;
  }

  [data-block="formulaire-relations"] .formula-card:nth-child(4),
  [data-block="formulaire-relations"] .formula-card:nth-child(5) {
    grid-column: span 3;
  }
}

/* =========================================================================
   25. ENCADRÉ « GRANDEURS ET UNITÉS » (paragraphe 7)
   -------------------------------------------------------------------------
   Carte bleu pastel, distincte du bloc orange des relations sans lui faire
   concurrence. Deux colonnes sur grand écran, une seule en dessous.
   ========================================================================= */

.course-block-quantities {
  background: var(--pastel-definition-bg);
  border: 1px solid var(--pastel-definition-border);
  border-left: 4px solid var(--pastel-definition-accent);
}

.course-block-quantities .course-block-title {
  color: var(--pastel-definition-accent);
}

.quantity-list {
  display: grid;
  gap: 0.15rem;
  margin: 0;
  padding: 0;
  list-style: none;
}

.quantity-row {
  display: grid;
  grid-template-columns: 3.4rem 1fr auto;
  align-items: baseline;
  gap: 0.6rem;
  padding: 0.45rem 0.6rem;
  border-radius: 8px;
  line-height: 1.45;
}

.quantity-row:nth-child(odd) {
  background: var(--surface);
}

.quantity-symbol {
  font-size: 1.05rem;
  font-weight: 800;
  color: var(--pastel-definition-accent);
}

.quantity-name {
  color: var(--text-primary);
}

.quantity-unit {
  color: var(--text-secondary);
  font-weight: 700;
  text-align: right;
}

.quantity-footnote {
  margin: 1.1rem 0 0 !important;
  padding-top: 0.9rem;
  color: var(--text-secondary);
  font-size: 0.92rem;
  border-top: 1px solid var(--pastel-definition-border);
}

@media (min-width: 900px) {
  /* Remplissage colonne par colonne : la lecture reste verticale. */
  .quantity-list {
    grid-auto-flow: column;
    grid-template-rows: repeat(6, auto);
    column-gap: 2rem;
  }
}

@media (max-width: 560px) {
  .quantity-row {
    grid-template-columns: 2.6rem 1fr;
    padding: 0.5rem;
  }

  .quantity-unit {
    grid-column: 2;
    text-align: left;
  }
}

/* =========================================================================
   26. ACTIVITÉS DU COURS (paragraphe 8)
   -------------------------------------------------------------------------
   Ton lavande. Composant autonome, sans rapport avec le questionnaire.
   ========================================================================= */

.course-block-activity {
  background: var(--pastel-example-bg);
  border: 1px solid var(--pastel-example-border);
  border-left: 4px solid var(--pastel-example-accent);
}

.course-block-activity .course-block-title {
  color: var(--pastel-example-accent);
}

.activity-instruction {
  margin: 0 0 1.5rem !important;
  color: var(--text-secondary);
  font-size: 1rem;
}

/* --- Réserve de grandeurs --- */

.activity-tray {
  display: flex;
  flex-wrap: wrap;
  gap: 0.85rem;
  justify-content: center;
  min-height: 88px;
  padding: 1rem;
  background: var(--surface);
  border: 2px dashed var(--pastel-example-border);
  border-radius: 16px;
}

.activity-tray.is-target,
.activity-slot.is-target {
  border-color: var(--pastel-example-accent);
  border-style: solid;
}

.activity-tray-hint {
  align-self: center;
  color: var(--text-secondary);
  font-size: 0.92rem;
}

/* --- Tuiles --- */

.activity-tile {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 72px;
  height: 56px;
  color: var(--pastel-example-accent);
  font-size: 1.5rem;
  font-weight: 800;
  cursor: grab;
  background: var(--surface);
  border: 2px solid var(--pastel-example-accent);
  border-radius: 14px;
  box-shadow: var(--shadow-card);
  touch-action: none;
  transition: transform 140ms ease, box-shadow 140ms ease;
}

.activity-tile:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-card-hover);
}

.activity-tile.is-selected {
  color: var(--text-on-accent);
  background: var(--pastel-example-accent);
}

.activity-tile:focus-visible {
  outline: 3px solid var(--focus-ring);
  outline-offset: 3px;
}

.activity-tile.is-dragging {
  opacity: 0.25;
}

.activity-tile-ghost {
  position: fixed;
  z-index: 50;
  pointer-events: none;
  transform: scale(1.05);
  box-shadow: var(--shadow);
}

/* --- Structure de la relation --- */

.activity-structure {
  display: grid;
  justify-items: center;
  gap: 0.75rem;
  margin: 2rem auto;
  max-width: 460px;
}

.activity-bar {
  width: 100%;
  height: 3px;
  background: var(--text-primary);
  border-radius: 3px;
}

.activity-bottom {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1.25rem;
  width: 100%;
}

.activity-slot {
  display: flex;
  align-items: center;
  justify-content: center;
  min-width: 96px;
  min-height: 76px;
  padding: 0.5rem;
  background: var(--surface);
  border: 2px dashed var(--border-strong);
  border-radius: 16px;
  transition: border-color 140ms ease;
}

.activity-slot.is-filled {
  border-style: solid;
  border-color: var(--pastel-example-border);
}

.activity-structure > .activity-slot {
  min-width: 132px;
}

/* --- Actions et retours --- */

.activity-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  justify-content: center;
}

.activity-feedback {
  margin: 1.5rem 0 0 !important;
  padding: 0.9rem 1.1rem;
  border: 1px solid transparent;
  border-radius: 12px;
  line-height: 1.55;
}

.activity-feedback-correct {
  color: var(--success);
  background: var(--success-bg);
  border-color: var(--success-border);
  font-weight: 700;
}

.activity-feedback-wrong {
  color: var(--error);
  background: var(--error-bg);
  border-color: var(--error-border);
}

/* --- Révélation des trois écritures --- */

.activity-reveal {
  margin-top: 1.5rem;
  padding-top: 1.25rem;
  border-top: 1px solid var(--pastel-example-border);
}

.activity-reveal-lead {
  margin: 0 0 1rem !important;
  color: var(--text-secondary);
}

.activity-reveal-formulas {
  display: grid;
  gap: 1rem;
  justify-items: center;
  margin-bottom: 1.25rem;
}

.activity-reveal-formulas .formula-line {
  padding: 0.7rem 1.4rem;
  background: var(--surface);
  border: 1px solid var(--pastel-example-border);
  border-radius: 12px;
  animation: activity-reveal 320ms ease both;
  animation-delay: var(--delay, 0ms);
}

@keyframes activity-reveal {
  from {
    opacity: 0;
    transform: translateY(6px);
  }
}

.activity-reveal-note {
  margin: 0 !important;
  color: var(--text-primary);
  line-height: 1.6;
}

@media (min-width: 900px) {
  .activity-structure {
    max-width: 560px;
  }

  .activity-reveal-formulas {
    grid-template-columns: repeat(3, minmax(0, 1fr));
    align-items: center;
  }
}

@media (max-width: 560px) {
  .activity-tile {
    width: 64px;
    height: 52px;
    font-size: 1.35rem;
  }

  .activity-slot {
    min-width: 76px;
    min-height: 68px;
  }

  .activity-bottom {
    gap: 0.75rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  .activity-reveal-formulas .formula-line {
    animation: none;
  }
}

/* =========================================================================
   27. ACTIVITÉ 2 — CONSTRUIRE LA RELATION DEMANDÉE
   ========================================================================= */

.build-goal {
  margin: 1.5rem 0 !important;
  font-size: clamp(1.05rem, 2.4vw, 1.2rem);
  font-weight: 700;
  line-height: 1.5;
  text-align: center;
}

/* --- Zone d'expression --- */

.build-expression {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 0.9rem;
  margin: 0 auto 1.75rem;
  padding: clamp(1.2rem, 3vw, 2rem);
  background: var(--surface);
  border: 1px solid var(--pastel-example-border);
  border-radius: 20px;
  box-shadow: var(--shadow-card);
}

.build-left {
  color: var(--text-heading);
  font-size: clamp(1.6rem, 4vw, 2rem);
  font-weight: 800;
}

.build-equals {
  color: var(--text-secondary);
  font-size: clamp(1.4rem, 3.5vw, 1.75rem);
}

.build-body {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.build-body[data-shape="fraction"] {
  flex-direction: column;
  gap: 0.5rem;
}

/* --- Emplacements --- */

.build-slot {
  display: flex;
  align-items: center;
  justify-content: center;
  min-width: 86px;
  min-height: 66px;
  padding: 0.35rem;
  background: var(--pastel-example-bg);
  border: 2px dashed var(--border-strong);
  border-radius: 14px;
  transition: border-color 140ms ease;
}

.build-slot.is-filled {
  border-style: solid;
  border-color: var(--pastel-example-border);
}

.build-slot.is-target {
  border-style: solid;
  border-color: var(--pastel-example-accent);
}

.build-slot-operator {
  min-width: 66px;
}

/* En fraction, l'opération devient la barre elle-même. */
.build-body[data-shape="fraction"] .build-slot-first,
.build-body[data-shape="fraction"] .build-slot-second {
  min-width: 132px;
}

.build-slot.is-bar {
  width: 100%;
  min-width: 0;
  min-height: 26px;
  padding: 0;
  background: transparent;
  border: 0;
}

.build-slot.is-bar .build-tile {
  width: 100%;
  height: 8px;
  min-height: 0;
  padding: 0;
  font-size: 0;
  color: transparent;
  background: var(--text-primary);
  border: 0;
  border-radius: 4px;
  box-shadow: none;
}

.build-slot.is-bar .build-tile:hover {
  transform: none;
  background: var(--pastel-example-accent);
}

/* --- Cartes --- */

.build-tray {
  display: flex;
  flex-wrap: wrap;
  gap: 0.85rem;
  justify-content: center;
  min-height: 84px;
  padding: 1rem;
  background: var(--surface);
  border: 2px dashed var(--pastel-example-border);
  border-radius: 16px;
}

.build-tray.is-target {
  border-style: solid;
  border-color: var(--pastel-example-accent);
}

.build-tile {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 74px;
  min-height: 56px;
  padding: 0 0.9rem;
  color: var(--pastel-example-accent);
  font-size: 1.4rem;
  font-weight: 800;
  cursor: grab;
  background: var(--surface);
  border: 2px solid var(--pastel-example-accent);
  border-radius: 14px;
  box-shadow: var(--shadow-card);
  touch-action: none;
  transition: transform 140ms ease, box-shadow 140ms ease, background 140ms ease;
}

.build-tile:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-card-hover);
}

.build-tile.is-selected {
  color: var(--text-on-accent);
  background: var(--pastel-example-accent);
}

.build-tile:focus-visible {
  outline: 3px solid var(--focus-ring);
  outline-offset: 3px;
}

.build-tile.is-dragging {
  opacity: 0.25;
}

.build-tile-operator {
  min-width: 62px;
  color: var(--text-secondary);
  border-color: var(--border-strong);
}

/* --- Relation validée et bilan --- */

.build-validated {
  display: flex;
  justify-content: center;
  margin-top: 1.25rem;
}

.build-validated .formula-line,
.build-summary-list .formula-line {
  padding: 0.7rem 1.4rem;
  background: var(--surface);
  border: 1px solid var(--pastel-example-border);
  border-radius: 12px;
  animation: activity-reveal 320ms ease both;
}

.build-summary-note {
  margin: 1rem 0 1.5rem !important;
  color: var(--text-primary);
  line-height: 1.6;
}

.build-summary-list {
  display: grid;
  gap: 0.9rem;
  justify-items: center;
  margin: 0 0 1.5rem;
  padding: 0;
  list-style: none;
}

@media (min-width: 900px) {
  .build-summary-list {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 560px) {
  .build-slot {
    min-width: 74px;
    min-height: 58px;
  }

  .build-body[data-shape="fraction"] .build-slot-first,
  .build-body[data-shape="fraction"] .build-slot-second {
    min-width: 112px;
  }

  .build-tile {
    min-width: 64px;
    min-height: 52px;
    font-size: 1.25rem;
  }
}