:root {
  --bg: #f7f9fc;
  --surface: #ffffff;
  --surface-soft: #f0f4ff;
  --text: #162033;
  --muted: #5f6b84;
  --primary: #355cde;
  --primary-dark: #2446b8;
  --secondary: #e9eefc;
  --border: #dbe3f2;
  --shadow: 0 12px 32px rgba(21, 34, 66, 0.08);
  --radius-xl: 24px;
  --radius-lg: 18px;
  --radius-md: 14px;
  --radius-sm: 10px;
  --container: 1000px;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: "Inter", Arial, sans-serif;
  background: linear-gradient(180deg, #ffffff 0%, #f7f9fc 100%);
  color: var(--text);
  line-height: 1.7;
}

a {
  text-decoration: none;
  color: inherit;
}

.container {
  width: min(var(--container), calc(100% - 2rem));
  margin: 0 auto;
}

/* Header */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}

.header-container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  padding: 1rem 0;
}

.site-title {
  margin: 0;
  font-size: 1.8rem;
  color: var(--primary);
  font-weight: 800;
}

.site-subtitle {
  margin: 0.25rem 0 0;
  color: var(--muted);
  font-size: 1rem;
}

.back-link {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.8rem 1rem;
  background: var(--secondary);
  color: var(--primary);
  font-weight: 700;
  border-radius: 12px;
  border: 1px solid var(--border);
  transition: 0.2s ease;
}

.back-link:hover {
  background: #dde6ff;
  transform: translateY(-1px);
}

/* Hero */
.hero {
  padding: 3rem 0 2rem;
}

.hero-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow);
  padding: 2rem;
}

.hero-card h1 {
  margin: 0 0 1rem;
  font-size: clamp(2rem, 4vw, 2.8rem);
  line-height: 1.15;
  color: var(--text);
}

.hero-card p {
  margin: 0;
  color: var(--muted);
  font-size: 1.05rem;
}

.hero-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.7rem;
  margin-top: 1.3rem;
}

.tag {
  display: inline-block;
  padding: 0.45rem 0.8rem;
  border-radius: 999px;
  background: rgba(53, 92, 222, 0.1);
  color: var(--primary);
  font-weight: 700;
  font-size: 0.9rem;
}

/* Main */
main.container {
  padding-bottom: 3rem;
}

.section {
  margin-bottom: 2.3rem;
}

.section h2 {
  font-size: 2rem;
  margin-bottom: 1rem;
  color: var(--text);
}

/* Cards / boxes */
.lesson-box,
.example-box,
.exercise-box,
.video-box,
.tip-box {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow);
  padding: 1.4rem;
  margin-bottom: 1.2rem;
}

.lesson-box h3,
.example-box h3,
.exercise-box h3 {
  margin-top: 0;
  margin-bottom: 0.8rem;
  color: var(--primary);
  font-size: 1.2rem;
}

.lesson-box p,
.example-box p,
.exercise-box p,
.video-box p,
.tip-box p {
  margin: 0.6rem 0;
}

/* Code */
pre {
  background: #0f172a;
  color: #e2e8f0;
  padding: 1rem;
  border-radius: 14px;
  overflow-x: auto;
  font-size: 0.95rem;
  line-height: 1.5;
  margin: 1rem 0;
}

code {
  font-family: Consolas, Monaco, "Courier New", monospace;
}

/* Video */
.video-box iframe {
  width: 100%;
  max-width: 100%;
  aspect-ratio: 16 / 9;
  border: 0;
  border-radius: 16px;
  margin-top: 1rem;
  display: block;
}

/* Special blocks */
.example-box {
  background: #f8fbff;
  border-left: 6px solid var(--primary);
}

.tip-box {
  background: #fffdf4;
  border-left: 6px solid #f2c94c;
}

/* Footer nav */
.footer-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  margin-top: 1.5rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.9rem 1.2rem;
  border-radius: 14px;
  font-weight: 700;
  border: 1px solid transparent;
  transition: 0.2s ease;
  cursor: pointer;
}

.btn:hover {
  transform: translateY(-1px);
}

.btn-primary {
  background: var(--primary);
  color: white;
}

.btn-primary:hover {
  background: var(--primary-dark);
}

.btn-secondary {
  background: var(--secondary);
  color: var(--primary);
  border-color: var(--border);
}

.btn-secondary:hover {
  background: #dde6ff;
}

/* Responsive */
@media (max-width: 768px) {
  .header-container {
    flex-direction: column;
    align-items: flex-start;
  }

  .hero {
    padding-top: 2rem;
  }

  .hero-card {
    padding: 1.4rem;
  }

  .section h2 {
    font-size: 1.6rem;
  }

  .footer-nav {
    flex-direction: column;
  }

  .btn,
  .back-link {
    width: 100%;
    text-align: center;
  }
}

/* ===== AJOUTS POUR MATH & LISTES ===== */

.math {
  display: inline-block;
  padding: 0.15rem 0.4rem;
  margin: 0 0.1rem;
  background: var(--surface-soft);
  color: var(--primary-dark);
  border: 1px solid var(--border);
  border-radius: 8px;
  font-family: Consolas, Monaco, "Courier New", monospace;
  font-weight: 700;
  white-space: nowrap;
}

.lesson-box ul,
.lesson-box ol,
.exercise-box ul,
.exercise-box ol {
  margin: 0.8rem 0 0.2rem;
  padding-left: 1.4rem;
}

.lesson-box li,
.exercise-box li {
  margin-bottom: 0.45rem;
}