/* ═══════════════════════════════════════════════════════════
   MATHIA TUNISIE — MASTER STYLESHEET
   Dark Tech Theme: Deep Navy + Teal/Cyan Accents
   ═══════════════════════════════════════════════════════════ */

/* ── CSS Variables ─────────────────────────────────────────── */
:root {
  /* Core Palette */
  --bg-primary:    #050d1a;
  --bg-secondary:  #080f1f;
  --bg-card:       #0a1628;
  --bg-card-hover: #0d1e35;
  --bg-elevated:   #0f2040;
  --bg-input:      #071020;

  /* Accent Colors */
  --accent-primary:  #00d4aa;
  --accent-secondary:#0099ff;
  --accent-glow:     rgba(0, 212, 170, 0.15);
  --accent-glow-blue:rgba(0, 153, 255, 0.12);

  /* Text */
  --text-primary:   #f0f6ff;
  --text-secondary: #8ba3c7;
  --text-muted:     #4a6080;
  --text-accent:    #00d4aa;

  /* Borders */
  --border-subtle:  rgba(0, 212, 170, 0.08);
  --border-normal:  rgba(0, 212, 170, 0.15);
  --border-strong:  rgba(0, 212, 170, 0.3);

  /* Gradients */
  --grad-primary:   linear-gradient(135deg, #00d4aa 0%, #0099ff 100%);
  --grad-dark:      linear-gradient(180deg, #050d1a 0%, #080f1f 100%);
  --grad-card:      linear-gradient(135deg, #0a1628 0%, #0d1e35 100%);
  --grad-hero:      radial-gradient(ellipse at 60% 40%, rgba(0,212,170,0.08) 0%, transparent 60%),
                    radial-gradient(ellipse at 20% 80%, rgba(0,153,255,0.06) 0%, transparent 50%);

  /* Shadows */
  --shadow-sm:   0 2px 8px rgba(0,0,0,0.4);
  --shadow-md:   0 8px 32px rgba(0,0,0,0.5);
  --shadow-lg:   0 20px 60px rgba(0,0,0,0.6);
  --shadow-glow: 0 0 30px rgba(0,212,170,0.2);
  --shadow-card: 0 4px 24px rgba(0,0,0,0.4), 0 0 0 1px rgba(0,212,170,0.08);

  /* Spacing */
  --nav-height: 72px;
  --radius-sm:  8px;
  --radius-md:  12px;
  --radius-lg:  16px;
  --radius-xl:  24px;

  /* Typography */
  --font-main:  'Inter', -apple-system, sans-serif;
  --font-mono:  'JetBrains Mono', 'Fira Code', monospace;

  /* Transitions */
  --transition: 0.25s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

/* ── Reset & Base ───────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html {
  scroll-behavior: smooth;
  scroll-padding-top: var(--nav-height);
}

body {
  font-family: var(--font-main);
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
}

a { color: inherit; text-decoration: none; }
button { cursor: pointer; border: none; background: none; font-family: inherit; }
input, textarea, select { font-family: inherit; }
img { max-width: 100%; display: block; }
ul { list-style: none; }

/* ── Scrollbar ──────────────────────────────────────────────── */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: var(--bg-secondary); }
::-webkit-scrollbar-thumb { background: var(--border-strong); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--accent-primary); }

/* ── Container ──────────────────────────────────────────────── */
.container {
  max-width: 1280px;
  margin: 0 auto;
  padding: 0 24px;
}

/* ── Utility ────────────────────────────────────────────────── */
.gradient-text {
  background: var(--grad-primary);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

/* ═══════════════════════════════════════════════════════════
   NAVIGATION
   ═══════════════════════════════════════════════════════════ */
.navbar {
  position: fixed;
  top: 0; left: 0; right: 0;
  z-index: 1000;
  height: var(--nav-height);
  background: rgba(5, 13, 26, 0.85);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border-subtle);
  transition: var(--transition);
}

.navbar.scrolled {
  background: rgba(5, 13, 26, 0.97);
  border-bottom-color: var(--border-normal);
  box-shadow: 0 4px 30px rgba(0,0,0,0.5);
}

.nav-container {
  max-width: 1280px;
  margin: 0 auto;
  padding: 0 24px;
  height: 100%;
  display: flex;
  align-items: center;
  gap: 32px;
}

.nav-logo {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-shrink: 0;
}

.logo-icon {
  width: 36px; height: 36px;
  background: var(--grad-primary);
  border-radius: 10px;
  display: flex; align-items: center; justify-content: center;
  color: #050d1a;
  box-shadow: 0 0 20px rgba(0,212,170,0.3);
}

.logo-icon svg { width: 20px; height: 20px; stroke-width: 2; }

.logo-text {
  font-size: 1.3rem;
  font-weight: 800;
  letter-spacing: -0.5px;
  color: var(--text-primary);
}

.logo-accent { color: var(--accent-primary); }

.logo-badge {
  font-size: 0.65rem;
  font-weight: 600;
  color: var(--accent-primary);
  background: rgba(0,212,170,0.1);
  border: 1px solid rgba(0,212,170,0.2);
  padding: 2px 8px;
  border-radius: 20px;
  letter-spacing: 0.5px;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 4px;
  flex: 1;
}

.nav-link {
  padding: 8px 16px;
  border-radius: var(--radius-sm);
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--text-secondary);
  transition: var(--transition);
  position: relative;
}

.nav-link:hover, .nav-link.active {
  color: var(--text-primary);
  background: rgba(0,212,170,0.08);
}

.nav-link.active { color: var(--accent-primary); }

.nav-link.active::after {
  content: '';
  position: absolute;
  bottom: -1px; left: 50%;
  transform: translateX(-50%);
  width: 20px; height: 2px;
  background: var(--accent-primary);
  border-radius: 1px;
}

.nav-actions {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-left: auto;
}

.nav-level-badge {
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--accent-secondary);
  background: rgba(0,153,255,0.1);
  border: 1px solid rgba(0,153,255,0.2);
  padding: 4px 12px;
  border-radius: 20px;
}

.hamburger {
  display: none;
  flex-direction: column;
  gap: 5px;
  padding: 8px;
  border-radius: var(--radius-sm);
  transition: var(--transition);
}

.hamburger span {
  display: block;
  width: 22px; height: 2px;
  background: var(--text-secondary);
  border-radius: 1px;
  transition: var(--transition);
}

.hamburger:hover span { background: var(--accent-primary); }

/* ═══════════════════════════════════════════════════════════
   HERO SECTION
   ═══════════════════════════════════════════════════════════ */
.hero {
  min-height: 100vh;
  display: flex;
  align-items: center;
  position: relative;
  overflow: hidden;
  padding: calc(var(--nav-height) + 60px) 24px 80px;
}

.hero-bg {
  position: absolute;
  inset: 0;
  pointer-events: none;
}

.hero-grid {
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(rgba(0,212,170,0.04) 1px, transparent 1px),
    linear-gradient(90deg, rgba(0,212,170,0.04) 1px, transparent 1px);
  background-size: 60px 60px;
  mask-image: radial-gradient(ellipse at center, black 30%, transparent 80%);
}

.hero-glow {
  position: absolute;
  border-radius: 50%;
  filter: blur(80px);
  pointer-events: none;
}

.glow-1 {
  width: 600px; height: 600px;
  background: radial-gradient(circle, rgba(0,212,170,0.12) 0%, transparent 70%);
  top: -100px; right: -100px;
  animation: glowPulse 6s ease-in-out infinite;
}

.glow-2 {
  width: 400px; height: 400px;
  background: radial-gradient(circle, rgba(0,153,255,0.1) 0%, transparent 70%);
  bottom: 0; left: 10%;
  animation: glowPulse 8s ease-in-out infinite reverse;
}

@keyframes glowPulse {
  0%, 100% { opacity: 0.6; transform: scale(1); }
  50% { opacity: 1; transform: scale(1.1); }
}

.hero-particles {
  position: absolute;
  inset: 0;
}

.hero-content {
  max-width: 1280px;
  margin: 0 auto;
  width: 100%;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 80px;
  align-items: center;
  position: relative;
  z-index: 1;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: rgba(0,212,170,0.08);
  border: 1px solid rgba(0,212,170,0.2);
  padding: 8px 16px;
  border-radius: 30px;
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--accent-primary);
  margin-bottom: 24px;
  width: fit-content;
  animation: fadeInUp 0.6s ease both;
}

.hero-badge svg { width: 14px; height: 14px; }

.hero-title {
  font-size: clamp(2.5rem, 5vw, 4rem);
  font-weight: 900;
  line-height: 1.1;
  letter-spacing: -2px;
  margin-bottom: 24px;
  animation: fadeInUp 0.6s 0.1s ease both;
}

.hero-subtitle {
  font-size: 1.1rem;
  color: var(--text-secondary);
  line-height: 1.7;
  margin-bottom: 36px;
  max-width: 500px;
  animation: fadeInUp 0.6s 0.2s ease both;
}

.hero-subtitle strong { color: var(--text-primary); }

.hero-cta {
  display: flex;
  gap: 16px;
  flex-wrap: wrap;
  margin-bottom: 48px;
  animation: fadeInUp 0.6s 0.3s ease both;
}

.btn-primary {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 14px 28px;
  background: var(--grad-primary);
  color: #050d1a;
  font-weight: 700;
  font-size: 0.95rem;
  border-radius: var(--radius-md);
  transition: var(--transition);
  box-shadow: 0 0 30px rgba(0,212,170,0.3);
  position: relative;
  overflow: hidden;
}

.btn-primary::before {
  content: '';
  position: absolute;
  inset: 0;
  background: rgba(255,255,255,0.1);
  opacity: 0;
  transition: var(--transition);
}

.btn-primary:hover::before { opacity: 1; }
.btn-primary:hover { transform: translateY(-2px); box-shadow: 0 0 40px rgba(0,212,170,0.4); }
.btn-primary svg { width: 18px; height: 18px; }

.btn-secondary {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 14px 28px;
  background: transparent;
  color: var(--text-primary);
  font-weight: 600;
  font-size: 0.95rem;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-normal);
  transition: var(--transition);
}

.btn-secondary:hover {
  background: rgba(0,212,170,0.08);
  border-color: var(--border-strong);
  transform: translateY(-2px);
}

.btn-secondary svg { width: 18px; height: 18px; }

.hero-stats {
  display: flex;
  align-items: center;
  gap: 24px;
  animation: fadeInUp 0.6s 0.4s ease both;
}

.stat-item { text-align: center; }

.stat-number {
  display: block;
  font-size: 1.6rem;
  font-weight: 800;
  color: var(--accent-primary);
  line-height: 1;
}

.stat-label {
  font-size: 0.75rem;
  color: var(--text-muted);
  font-weight: 500;
  margin-top: 4px;
}

.stat-divider {
  width: 1px;
  height: 40px;
  background: var(--border-subtle);
}

/* Hero Card */
.hero-visual {
  display: flex;
  justify-content: center;
  align-items: center;
  animation: fadeInRight 0.8s 0.3s ease both;
}

.hero-card {
  background: var(--bg-card);
  border: 1px solid var(--border-normal);
  border-radius: var(--radius-xl);
  padding: 24px;
  width: 100%;
  max-width: 420px;
  box-shadow: var(--shadow-lg), var(--shadow-glow);
  font-family: var(--font-mono);
  font-size: 0.85rem;
}

.card-header {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 20px;
  padding-bottom: 16px;
  border-bottom: 1px solid var(--border-subtle);
  font-size: 0.8rem;
  color: var(--text-muted);
}

.card-dot {
  width: 12px; height: 12px;
  border-radius: 50%;
}

.card-dot.green  { background: #00d4aa; box-shadow: 0 0 8px rgba(0,212,170,0.5); }
.card-dot.yellow { background: #ffd700; }
.card-dot.red    { background: #ff5f57; }

.code-line {
  padding: 4px 0;
  line-height: 1.8;
}

.code-comment { color: var(--text-muted); font-style: italic; }
.code-key { color: var(--accent-secondary); }
.code-val { color: var(--text-primary); }
.code-line.success .code-key { color: var(--accent-primary); }
.code-line.success .code-val { color: var(--accent-primary); font-weight: 600; }

.floating {
  animation: float 4s ease-in-out infinite;
}

@keyframes float {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-12px); }
}

/* ═══════════════════════════════════════════════════════════
   FEATURES STRIP
   ═══════════════════════════════════════════════════════════ */
.features-strip {
  padding: 40px 24px;
  background: var(--bg-secondary);
  border-top: 1px solid var(--border-subtle);
  border-bottom: 1px solid var(--border-subtle);
}

.features-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 24px;
}

.feature-card {
  display: flex;
  align-items: center;
  gap: 16px;
  padding: 20px;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  transition: var(--transition);
}

.feature-card:hover {
  border-color: var(--border-normal);
  background: var(--bg-card-hover);
  transform: translateY(-2px);
}

.feature-icon {
  width: 44px; height: 44px;
  background: rgba(0,212,170,0.1);
  border: 1px solid rgba(0,212,170,0.2);
  border-radius: var(--radius-sm);
  display: flex; align-items: center; justify-content: center;
  color: var(--accent-primary);
  flex-shrink: 0;
}

.feature-icon svg { width: 20px; height: 20px; }

.feature-text h3 {
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 4px;
}

.feature-text p {
  font-size: 0.78rem;
  color: var(--text-muted);
  line-height: 1.4;
}

/* ═══════════════════════════════════════════════════════════
   SECTIONS COMMON
   ═══════════════════════════════════════════════════════════ */
.section {
  padding: 100px 24px;
}

.section-alt {
  background: var(--bg-secondary);
}

.section-header {
  text-align: center;
  margin-bottom: 60px;
}

.section-badge {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: rgba(0,212,170,0.08);
  border: 1px solid rgba(0,212,170,0.2);
  padding: 6px 16px;
  border-radius: 30px;
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--accent-primary);
  margin-bottom: 16px;
  letter-spacing: 0.5px;
  text-transform: uppercase;
}

.section-badge svg { width: 14px; height: 14px; }

.section-title {
  font-size: clamp(2rem, 4vw, 3rem);
  font-weight: 900;
  letter-spacing: -1.5px;
  margin-bottom: 16px;
  line-height: 1.1;
}

.section-subtitle {
  font-size: 1rem;
  color: var(--text-secondary);
  max-width: 600px;
  margin: 0 auto;
  line-height: 1.7;
}

/* ═══════════════════════════════════════════════════════════
   AI SOLVER
   ═══════════════════════════════════════════════════════════ */
.solver-layout {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 32px;
  align-items: start;
}

.panel-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-xl);
  padding: 28px;
  box-shadow: var(--shadow-card);
  transition: var(--transition);
}

.panel-card:hover {
  border-color: var(--border-normal);
}

/* Tabs */
.panel-tabs {
  display: flex;
  gap: 8px;
  margin-bottom: 24px;
  background: var(--bg-input);
  padding: 4px;
  border-radius: var(--radius-md);
}

.tab-btn {
  flex: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 10px 16px;
  border-radius: var(--radius-sm);
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--text-muted);
  transition: var(--transition);
}

.tab-btn.active {
  background: var(--bg-elevated);
  color: var(--accent-primary);
  box-shadow: var(--shadow-sm);
}

.tab-btn svg { width: 16px; height: 16px; }

.tab-content { display: none; }
.tab-content.active { display: block; }

/* Input Elements */
.input-label {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: 10px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.input-label svg { width: 14px; height: 14px; color: var(--accent-primary); }

.input-group { margin-bottom: 20px; }

.problem-textarea {
  width: 100%;
  background: var(--bg-input);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: 16px;
  color: var(--text-primary);
  font-size: 0.92rem;
  line-height: 1.6;
  resize: vertical;
  min-height: 140px;
  transition: var(--transition);
  outline: none;
}

.problem-textarea:focus {
  border-color: var(--border-strong);
  box-shadow: 0 0 0 3px rgba(0,212,170,0.08);
}

.problem-textarea::placeholder { color: var(--text-muted); }

.level-selector, .topic-selector { margin-bottom: 20px; }

.level-btns {
  display: flex;
  gap: 8px;
}

.level-btn {
  flex: 1;
  padding: 10px 16px;
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text-muted);
  background: var(--bg-input);
  border: 1px solid var(--border-subtle);
  transition: var(--transition);
}

.level-btn.active, .level-btn:hover {
  color: var(--accent-primary);
  border-color: var(--border-strong);
  background: rgba(0,212,170,0.08);
}

.topic-select {
  width: 100%;
  background: var(--bg-input);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: 12px 16px;
  color: var(--text-primary);
  font-size: 0.9rem;
  outline: none;
  transition: var(--transition);
  appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 24 24' fill='none' stroke='%2300d4aa' stroke-width='2'%3E%3Cpath d='m6 9 6 6 6-6'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 12px center;
  padding-right: 40px;
}

.topic-select:focus { border-color: var(--border-strong); }
.topic-select option { background: var(--bg-card); }

/* Image Upload */
.image-upload-zone {
  border: 2px dashed var(--border-normal);
  border-radius: var(--radius-lg);
  padding: 40px 24px;
  text-align: center;
  transition: var(--transition);
  cursor: pointer;
  min-height: 200px;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 12px;
  position: relative;
  overflow: hidden;
}

.image-upload-zone:hover, .image-upload-zone.drag-over {
  border-color: var(--accent-primary);
  background: rgba(0,212,170,0.04);
}

.upload-icon {
  width: 56px; height: 56px;
  background: rgba(0,212,170,0.1);
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  margin: 0 auto 16px;
  color: var(--accent-primary);
}

.upload-icon svg { width: 28px; height: 28px; }

.upload-title {
  font-size: 1rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 6px;
}

.upload-sub {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-bottom: 8px;
}

.upload-formats {
  font-size: 0.75rem;
  color: var(--text-muted);
  margin-bottom: 20px;
}

.btn-upload {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 20px;
  background: rgba(0,212,170,0.1);
  border: 1px solid var(--border-normal);
  border-radius: var(--radius-sm);
  color: var(--accent-primary);
  font-size: 0.85rem;
  font-weight: 600;
  transition: var(--transition);
}

.btn-upload:hover {
  background: rgba(0,212,170,0.2);
  border-color: var(--border-strong);
}

.btn-upload svg { width: 16px; height: 16px; }

.upload-preview {
  position: relative;
  width: 100%;
}

.upload-preview img {
  width: 100%;
  max-height: 200px;
  object-fit: contain;
  border-radius: var(--radius-md);
}

.remove-img {
  position: absolute;
  top: 8px; right: 8px;
  width: 28px; height: 28px;
  background: rgba(255,95,87,0.9);
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  color: white;
  transition: var(--transition);
}

.remove-img:hover { background: #ff5f57; transform: scale(1.1); }
.remove-img svg { width: 14px; height: 14px; }

.upload-hint {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.78rem;
  color: var(--text-muted);
}

.upload-hint svg { width: 14px; height: 14px; color: var(--accent-secondary); flex-shrink: 0; }

/* Solve Button */
.btn-solve {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  padding: 16px 24px;
  background: var(--grad-primary);
  color: #050d1a;
  font-size: 1rem;
  font-weight: 800;
  border-radius: var(--radius-md);
  margin-top: 24px;
  transition: var(--transition);
  position: relative;
  overflow: hidden;
  box-shadow: 0 0 30px rgba(0,212,170,0.25);
}

.btn-solve:hover {
  transform: translateY(-2px);
  box-shadow: 0 0 40px rgba(0,212,170,0.4);
}

.btn-solve:active { transform: translateY(0); }
.btn-solve svg { width: 20px; height: 20px; }

.btn-shine {
  position: absolute;
  top: 0; left: -100%;
  width: 60%;
  height: 100%;
  background: linear-gradient(90deg, transparent, rgba(255,255,255,0.2), transparent);
  transform: skewX(-20deg);
  animation: shine 3s infinite;
}

@keyframes shine {
  0% { left: -100%; }
  50%, 100% { left: 150%; }
}

.btn-solve.loading {
  pointer-events: none;
  opacity: 0.8;
}

/* Output Panel */
.output-card {
  min-height: 400px;
  display: flex;
  flex-direction: column;
}

.output-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 20px;
  padding-bottom: 16px;
  border-bottom: 1px solid var(--border-subtle);
}

.output-title {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 0.9rem;
  font-weight: 700;
  color: var(--accent-primary);
}

.output-title svg { width: 18px; height: 18px; }

.output-actions {
  display: flex;
  gap: 8px;
}

.action-btn {
  width: 32px; height: 32px;
  display: flex; align-items: center; justify-content: center;
  background: var(--bg-input);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  transition: var(--transition);
}

.action-btn:hover {
  color: var(--accent-primary);
  border-color: var(--border-normal);
}

.action-btn svg { width: 14px; height: 14px; }

.output-body {
  flex: 1;
  overflow-y: auto;
}

.output-placeholder {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  height: 300px;
  gap: 16px;
}

.placeholder-icon {
  width: 64px; height: 64px;
  background: rgba(0,212,170,0.08);
  border: 1px solid rgba(0,212,170,0.15);
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  color: var(--text-muted);
}

.placeholder-icon svg { width: 32px; height: 32px; }

.output-placeholder p {
  color: var(--text-secondary);
  font-size: 0.9rem;
  max-width: 280px;
}

.placeholder-sub {
  color: var(--text-muted) !important;
  font-size: 0.8rem !important;
}

/* Solution Display */
.solution-container {
  animation: fadeInUp 0.4s ease;
}

.solution-problem {
  background: var(--bg-input);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  padding: 16px;
  margin-bottom: 20px;
}

.solution-problem-label {
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--accent-secondary);
  text-transform: uppercase;
  letter-spacing: 1px;
  margin-bottom: 8px;
}

.solution-problem-text {
  font-size: 0.95rem;
  color: var(--text-primary);
  font-weight: 500;
}

.solution-type-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: rgba(0,212,170,0.1);
  border: 1px solid rgba(0,212,170,0.2);
  padding: 4px 12px;
  border-radius: 20px;
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--accent-primary);
  margin-bottom: 20px;
}

.solution-steps { display: flex; flex-direction: column; gap: 16px; }

.step-item {
  display: flex;
  gap: 16px;
  animation: fadeInUp 0.3s ease both;
}

.step-number {
  width: 28px; height: 28px;
  background: var(--grad-primary);
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  font-size: 0.75rem;
  font-weight: 800;
  color: #050d1a;
  flex-shrink: 0;
  margin-top: 2px;
}

.step-content { flex: 1; }

.step-title {
  font-size: 0.88rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 8px;
}

.step-body {
  font-size: 0.88rem;
  color: var(--text-secondary);
  line-height: 1.7;
}

.step-math {
  display: block;
  background: var(--bg-input);
  border: 1px solid var(--border-subtle);
  border-left: 3px solid var(--accent-primary);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  padding: 10px 14px;
  margin: 8px 0;
  font-family: var(--font-mono);
  font-size: 0.9rem;
  color: var(--accent-primary);
}

.solution-answer {
  background: linear-gradient(135deg, rgba(0,212,170,0.1), rgba(0,153,255,0.08));
  border: 1px solid rgba(0,212,170,0.3);
  border-radius: var(--radius-md);
  padding: 20px;
  margin-top: 20px;
  text-align: center;
}

.answer-label {
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--accent-primary);
  text-transform: uppercase;
  letter-spacing: 1px;
  margin-bottom: 8px;
}

.answer-value {
  font-size: 1.3rem;
  font-weight: 800;
  color: var(--text-primary);
  font-family: var(--font-mono);
}

/* Loading Animation */
.loading-dots {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 40px;
}

.loading-dots span {
  width: 8px; height: 8px;
  background: var(--accent-primary);
  border-radius: 50%;
  animation: dotBounce 1.4s ease-in-out infinite;
}

.loading-dots span:nth-child(2) { animation-delay: 0.2s; }
.loading-dots span:nth-child(3) { animation-delay: 0.4s; }

@keyframes dotBounce {
  0%, 80%, 100% { transform: scale(0.6); opacity: 0.4; }
  40% { transform: scale(1); opacity: 1; }
}

/* Quick Examples */
.quick-examples {
  margin-top: 20px;
  padding: 20px;
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
}

.examples-title {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: 12px;
}

.examples-title svg { width: 14px; height: 14px; color: #ffd700; }

.examples-grid {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.example-chip {
  padding: 6px 14px;
  background: var(--bg-input);
  border: 1px solid var(--border-subtle);
  border-radius: 20px;
  font-size: 0.8rem;
  font-weight: 500;
  color: var(--text-secondary);
  transition: var(--transition);
  font-family: var(--font-mono);
}

.example-chip:hover {
  color: var(--accent-primary);
  border-color: var(--border-normal);
  background: rgba(0,212,170,0.06);
}

/* ═══════════════════════════════════════════════════════════
   CALCULATOR
   ═══════════════════════════════════════════════════════════ */
.calc-layout {
  display: grid;
  grid-template-columns: 400px 1fr;
  gap: 40px;
  align-items: start;
}

.calc-wrapper {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-xl);
  overflow: hidden;
  box-shadow: var(--shadow-card);
}

.calc-display {
  background: var(--bg-input);
  padding: 24px 20px 20px;
  text-align: right;
  border-bottom: 1px solid var(--border-subtle);
}

.calc-expression {
  font-size: 0.85rem;
  color: var(--text-muted);
  font-family: var(--font-mono);
  min-height: 20px;
  margin-bottom: 8px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.calc-result {
  font-size: 2.5rem;
  font-weight: 700;
  color: var(--text-primary);
  font-family: var(--font-mono);
  line-height: 1;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.calc-modes {
  display: flex;
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border-subtle);
}

.calc-mode {
  flex: 1;
  padding: 10px;
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-muted);
  transition: var(--transition);
  border-bottom: 2px solid transparent;
}

.calc-mode.active {
  color: var(--accent-primary);
  border-bottom-color: var(--accent-primary);
  background: rgba(0,212,170,0.05);
}

.calc-scientific {
  display: grid;
  grid-template-columns: repeat(6, 1fr);
  gap: 1px;
  background: var(--border-subtle);
  border-bottom: 1px solid var(--border-subtle);
}

.calc-buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1px;
  background: var(--border-subtle);
}

.calc-btn {
  padding: 18px 12px;
  font-size: 1rem;
  font-weight: 600;
  transition: var(--transition);
  display: flex;
  align-items: center;
  justify-content: center;
}

.calc-btn.sci {
  padding: 12px 8px;
  font-size: 0.8rem;
  font-family: var(--font-mono);
}

.calc-btn.num {
  background: var(--bg-card);
  color: var(--text-primary);
}

.calc-btn.num:hover { background: var(--bg-card-hover); }

.calc-btn.op {
  background: rgba(0,153,255,0.1);
  color: var(--accent-secondary);
  font-size: 1.2rem;
}

.calc-btn.op:hover { background: rgba(0,153,255,0.2); }

.calc-btn.func {
  background: var(--bg-elevated);
  color: var(--text-secondary);
}

.calc-btn.func:hover { background: rgba(255,255,255,0.08); }

.calc-btn.equals {
  background: var(--grad-primary);
  color: #050d1a;
  font-size: 1.3rem;
}

.calc-btn.equals:hover { filter: brightness(1.1); }

.calc-btn.sci {
  background: var(--bg-elevated);
  color: var(--accent-primary);
}

.calc-btn.sci:hover { background: rgba(0,212,170,0.15); }

.calc-btn.zero { grid-column: span 1; }

.calc-btn:active { transform: scale(0.95); }

/* History */
.calc-history {
  padding: 16px;
  border-top: 1px solid var(--border-subtle);
  max-height: 180px;
  overflow-y: auto;
}

.history-header {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--text-muted);
  margin-bottom: 12px;
}

.history-header svg { width: 14px; height: 14px; }

.clear-hist {
  margin-left: auto;
  font-size: 0.72rem;
  color: var(--text-muted);
  padding: 2px 8px;
  border-radius: 4px;
  border: 1px solid var(--border-subtle);
  transition: var(--transition);
}

.clear-hist:hover { color: #ff5f57; border-color: rgba(255,95,87,0.3); }

.history-empty {
  font-size: 0.8rem;
  color: var(--text-muted);
  text-align: center;
  padding: 8px;
}

.history-entry {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 6px 8px;
  border-radius: var(--radius-sm);
  font-size: 0.82rem;
  font-family: var(--font-mono);
  transition: var(--transition);
  cursor: pointer;
}

.history-entry:hover { background: var(--bg-elevated); }

.history-expr { color: var(--text-muted); }
.history-res { color: var(--accent-primary); font-weight: 600; }

/* Formulas Panel */
.formulas-panel {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-xl);
  padding: 28px;
  box-shadow: var(--shadow-card);
}

.formulas-title {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 1rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 24px;
  padding-bottom: 16px;
  border-bottom: 1px solid var(--border-subtle);
}

.formulas-title svg { width: 18px; height: 18px; color: var(--accent-primary); }

.formula-group { margin-bottom: 24px; }

.formula-group h4 {
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--accent-secondary);
  text-transform: uppercase;
  letter-spacing: 1px;
  margin-bottom: 12px;
}

.formula-item {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 10px 12px;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-subtle);
  margin-bottom: 6px;
  transition: var(--transition);
  background: var(--bg-input);
}

.formula-item:hover {
  border-color: var(--border-normal);
  background: var(--bg-elevated);
}

.formula-name {
  font-size: 0.82rem;
  color: var(--text-secondary);
}

.formula-expr {
  font-size: 0.85rem;
  font-family: var(--font-mono);
  color: var(--accent-primary);
  font-weight: 600;
}

/* ═══════════════════════════════════════════════════════════
   EXERCISES
   ═══════════════════════════════════════════════════════════ */
.exercises-filters {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 16px;
  margin-bottom: 40px;
}

.filter-group, .filter-level {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.filter-btn, .level-filter {
  padding: 8px 18px;
  border-radius: 30px;
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--text-muted);
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  transition: var(--transition);
}

.filter-btn.active, .filter-btn:hover,
.level-filter.active, .level-filter:hover {
  color: var(--accent-primary);
  border-color: var(--border-strong);
  background: rgba(0,212,170,0.08);
}

.exercises-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 24px;
}

.exercise-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 24px;
  transition: var(--transition);
  cursor: pointer;
  position: relative;
  overflow: hidden;
}

.exercise-card::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 3px;
  background: var(--grad-primary);
  transform: scaleX(0);
  transform-origin: left;
  transition: var(--transition);
}

.exercise-card:hover {
  border-color: var(--border-normal);
  transform: translateY(-4px);
  box-shadow: var(--shadow-md), var(--shadow-glow);
}

.exercise-card:hover::before { transform: scaleX(1); }

.exercise-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  margin-bottom: 16px;
}

.exercise-tags {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
}

.exercise-tag {
  padding: 3px 10px;
  border-radius: 20px;
  font-size: 0.7rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.tag-equations  { background: rgba(0,212,170,0.1); color: var(--accent-primary); border: 1px solid rgba(0,212,170,0.2); }
.tag-geometrie  { background: rgba(0,153,255,0.1); color: var(--accent-secondary); border: 1px solid rgba(0,153,255,0.2); }
.tag-fonctions  { background: rgba(255,215,0,0.1); color: #ffd700; border: 1px solid rgba(255,215,0,0.2); }
.tag-vecteurs   { background: rgba(255,100,150,0.1); color: #ff6496; border: 1px solid rgba(255,100,150,0.2); }
.tag-statistiques { background: rgba(150,100,255,0.1); color: #9664ff; border: 1px solid rgba(150,100,255,0.2); }
.tag-trigonometrie { background: rgba(255,150,50,0.1); color: #ff9632; border: 1px solid rgba(255,150,50,0.2); }

.difficulty-badge {
  padding: 3px 10px;
  border-radius: 20px;
  font-size: 0.7rem;
  font-weight: 700;
}

.diff-facile  { background: rgba(0,212,170,0.1); color: var(--accent-primary); }
.diff-moyen   { background: rgba(255,215,0,0.1); color: #ffd700; }
.diff-difficile { background: rgba(255,95,87,0.1); color: #ff5f57; }

.exercise-level {
  font-size: 0.7rem;
  color: var(--text-muted);
  font-weight: 600;
  margin-bottom: 8px;
}

.exercise-title {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 10px;
  line-height: 1.4;
}

.exercise-preview {
  font-size: 0.85rem;
  color: var(--text-secondary);
  line-height: 1.6;
  margin-bottom: 16px;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.exercise-footer {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.exercise-solve-btn {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 8px 16px;
  background: rgba(0,212,170,0.1);
  border: 1px solid rgba(0,212,170,0.2);
  border-radius: var(--radius-sm);
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--accent-primary);
  transition: var(--transition);
}

.exercise-solve-btn:hover {
  background: rgba(0,212,170,0.2);
  border-color: var(--border-strong);
}

.exercise-solve-btn svg { width: 14px; height: 14px; }

/* Modal */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(5,13,26,0.9);
  backdrop-filter: blur(8px);
  z-index: 2000;
  display: none;
  align-items: center;
  justify-content: center;
  padding: 24px;
}

.modal-overlay.open { display: flex; }

.modal-card {
  background: var(--bg-card);
  border: 1px solid var(--border-normal);
  border-radius: var(--radius-xl);
  padding: 36px;
  max-width: 680px;
  width: 100%;
  max-height: 85vh;
  overflow-y: auto;
  position: relative;
  box-shadow: var(--shadow-lg), var(--shadow-glow);
  animation: modalIn 0.3s ease;
}

@keyframes modalIn {
  from { opacity: 0; transform: scale(0.95) translateY(20px); }
  to { opacity: 1; transform: scale(1) translateY(0); }
}

.modal-close {
  position: absolute;
  top: 16px; right: 16px;
  width: 32px; height: 32px;
  display: flex; align-items: center; justify-content: center;
  background: var(--bg-elevated);
  border-radius: 50%;
  color: var(--text-muted);
  transition: var(--transition);
}

.modal-close:hover { color: var(--text-primary); background: rgba(255,95,87,0.2); }
.modal-close svg { width: 16px; height: 16px; }

/* ═══════════════════════════════════════════════════════════
   ENIGMES
   ═══════════════════════════════════════════════════════════ */
.enigmes-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(340px, 1fr));
  gap: 28px;
}

.enigme-card {
  background: var(--bg-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-xl);
  padding: 28px;
  transition: var(--transition);
  position: relative;
  overflow: hidden;
}

.enigme-card::after {
  content: '';
  position: absolute;
  bottom: 0; right: 0;
  width: 120px; height: 120px;
  background: radial-gradient(circle, rgba(0,212,170,0.06) 0%, transparent 70%);
  pointer-events: none;
}

.enigme-card:hover {
  border-color: var(--border-normal);
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
}

.enigme-number {
  font-size: 0.72rem;
  font-weight: 700;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 1px;
  margin-bottom: 12px;
}

.enigme-title {
  font-size: 1.05rem;
  font-weight: 800;
  color: var(--text-primary);
  margin-bottom: 12px;
  line-height: 1.3;
}

.enigme-text {
  font-size: 0.88rem;
  color: var(--text-secondary);
  line-height: 1.7;
  margin-bottom: 20px;
}

.enigme-hint-btn {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 16px;
  background: rgba(255,215,0,0.08);
  border: 1px solid rgba(255,215,0,0.2);
  border-radius: var(--radius-sm);
  font-size: 0.8rem;
  font-weight: 600;
  color: #ffd700;
  transition: var(--transition);
  margin-bottom: 12px;
}

.enigme-hint-btn:hover { background: rgba(255,215,0,0.15); }
.enigme-hint-btn svg { width: 14px; height: 14px; }

.enigme-hint {
  background: rgba(255,215,0,0.05);
  border: 1px solid rgba(255,215,0,0.15);
  border-radius: var(--radius-sm);
  padding: 12px;
  font-size: 0.82rem;
  color: var(--text-secondary);
  display: none;
  margin-bottom: 12px;
}

.enigme-hint.visible { display: block; animation: fadeInUp 0.3s ease; }

.enigme-answer-btn {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 16px;
  background: rgba(0,212,170,0.08);
  border: 1px solid rgba(0,212,170,0.2);
  border-radius: var(--radius-sm);
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--accent-primary);
  transition: var(--transition);
}

.enigme-answer-btn:hover { background: rgba(0,212,170,0.15); }
.enigme-answer-btn svg { width: 14px; height: 14px; }

.enigme-answer {
  background: rgba(0,212,170,0.06);
  border: 1px solid rgba(0,212,170,0.2);
  border-radius: var(--radius-sm);
  padding: 12px;
  font-size: 0.85rem;
  color: var(--accent-primary);
  font-family: var(--font-mono);
  font-weight: 600;
  display: none;
  margin-top: 12px;
}

.enigme-answer.visible { display: block; animation: fadeInUp 0.3s ease; }

.enigme-difficulty {
  position: absolute;
  top: 20px; right: 20px;
  font-size: 1.2rem;
}

/* ═══════════════════════════════════════════════════════════
   FOOTER
   ═══════════════════════════════════════════════════════════ */
.footer {
  background: var(--bg-secondary);
  border-top: 1px solid var(--border-subtle);
  padding: 80px 24px 40px;
  position: relative;
  overflow: hidden;
}

.footer-glow {
  position: absolute;
  top: 0; left: 50%;
  transform: translateX(-50%);
  width: 600px; height: 200px;
  background: radial-gradient(ellipse, rgba(0,212,170,0.05) 0%, transparent 70%);
  pointer-events: none;
}

.footer-grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1.5fr;
  gap: 48px;
  margin-bottom: 48px;
}

.footer-brand .nav-logo { margin-bottom: 16px; }

.footer-desc {
  font-size: 0.85rem;
  color: var(--text-muted);
  line-height: 1.7;
  max-width: 280px;
}

.footer-links h4 {
  font-size: 0.82rem;
  font-weight: 700;
  color: var(--text-primary);
  text-transform: uppercase;
  letter-spacing: 1px;
  margin-bottom: 16px;
}

.footer-links ul { display: flex; flex-direction: column; gap: 10px; }

.footer-links a {
  font-size: 0.85rem;
  color: var(--text-muted);
  transition: var(--transition);
}

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

.footer-info h4 {
  font-size: 0.82rem;
  font-weight: 700;
  color: var(--text-primary);
  text-transform: uppercase;
  letter-spacing: 1px;
  margin-bottom: 12px;
}

.footer-info p {
  font-size: 0.82rem;
  color: var(--text-muted);
  line-height: 1.6;
  margin-bottom: 16px;
}

.footer-badges { display: flex; flex-direction: column; gap: 8px; }

.footer-badge-item {
  display: inline-block;
  padding: 4px 12px;
  background: rgba(0,212,170,0.08);
  border: 1px solid rgba(0,212,170,0.15);
  border-radius: 20px;
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--accent-primary);
  width: fit-content;
}

.footer-bottom {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-top: 32px;
  border-top: 1px solid var(--border-subtle);
  font-size: 0.8rem;
  color: var(--text-muted);
}

.footer-tagline { color: var(--text-muted); }

/* ═══════════════════════════════════════════════════════════
   TOAST
   ═══════════════════════════════════════════════════════════ */
.toast {
  position: fixed;
  bottom: 24px; right: 24px;
  background: var(--bg-elevated);
  border: 1px solid var(--border-normal);
  border-radius: var(--radius-md);
  padding: 14px 20px;
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--text-primary);
  box-shadow: var(--shadow-lg);
  z-index: 9999;
  transform: translateY(100px);
  opacity: 0;
  transition: var(--transition);
  max-width: 320px;
}

.toast.show {
  transform: translateY(0);
  opacity: 1;
}

.toast.success { border-color: rgba(0,212,170,0.4); color: var(--accent-primary); }
.toast.error   { border-color: rgba(255,95,87,0.4); color: #ff5f57; }

/* ═══════════════════════════════════════════════════════════
   ANIMATIONS
   ═══════════════════════════════════════════════════════════ */
@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(20px); }
  to   { opacity: 1; transform: translateY(0); }
}

@keyframes fadeInRight {
  from { opacity: 0; transform: translateX(30px); }
  to   { opacity: 1; transform: translateX(0); }
}

.animate-in {
  animation: fadeInUp 0.6s ease both;
}

/* ═══════════════════════════════════════════════════════════
   RESPONSIVE
   ═══════════════════════════════════════════════════════════ */
@media (max-width: 1100px) {
  .hero-content { grid-template-columns: 1fr; gap: 48px; }
  .hero-visual { display: none; }
  .calc-layout { grid-template-columns: 1fr; }
  .calc-wrapper { max-width: 400px; margin: 0 auto; }
  .footer-grid { grid-template-columns: 1fr 1fr; gap: 32px; }
}

@media (max-width: 900px) {
  .solver-layout { grid-template-columns: 1fr; }
  .features-grid { grid-template-columns: repeat(2, 1fr); }
  .nav-links { display: none; }
  .nav-links.open {
    display: flex;
    flex-direction: column;
    position: fixed;
    top: var(--nav-height);
    left: 0; right: 0;
    background: rgba(5,13,26,0.98);
    backdrop-filter: blur(20px);
    padding: 24px;
    border-bottom: 1px solid var(--border-subtle);
    gap: 4px;
    z-index: 999;
  }
  .hamburger { display: flex; }
  .nav-level-badge { display: none; }
}

@media (max-width: 640px) {
  .section { padding: 60px 16px; }
  .hero { padding: calc(var(--nav-height) + 40px) 16px 60px; }
  .hero-title { font-size: 2.2rem; letter-spacing: -1px; }
  .hero-cta { flex-direction: column; }
  .btn-primary, .btn-secondary { width: 100%; justify-content: center; }
  .features-grid { grid-template-columns: 1fr; }
  .exercises-filters { flex-direction: column; align-items: flex-start; }
  .footer-grid { grid-template-columns: 1fr; }
  .footer-bottom { flex-direction: column; gap: 8px; text-align: center; }
  .calc-scientific { grid-template-columns: repeat(4, 1fr); }
  .enigmes-grid { grid-template-columns: 1fr; }
  .exercises-grid { grid-template-columns: 1fr; }
}