/* ============================
   MARKUP QUEST — STYLE SYSTEM
   ============================ */

/* === RESET === */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html {
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
  scroll-behavior: smooth;
  scroll-padding-top: 5rem;
}
body {
  min-height: 100dvh;
  line-height: 1.6;
  font-family: 'Satoshi', 'Inter', system-ui, sans-serif;
  font-size: 16px;
  color: var(--color-text);
  background: var(--color-bg);
  overflow-x: hidden;
}
img, svg { display: block; max-width: 100%; }
ul[role='list'], ol[role='list'] { list-style: none; }
input, button, textarea, select { font: inherit; color: inherit; }
button { cursor: pointer; background: none; border: none; }
a { color: var(--color-primary); text-decoration: none; }
a:hover { text-decoration: underline; }
h1,h2,h3,h4,h5,h6 { line-height: 1.2; }
p, li { max-width: 72ch; }

/* === DESIGN TOKENS === */
:root, [data-theme='light'] {
  --color-bg: #f5f4f0;
  --color-surface: #edecea;
  --color-surface-2: #e4e3df;
  --color-surface-code: #dddcd8;
  --color-border: #c8c6c0;
  --color-text: #1e1d1a;
  --color-text-muted: #6b6a66;
  --color-text-faint: #9e9d99;
  --color-primary: #0e7a80;
  --color-primary-hover: #0a5c61;
  --color-primary-bg: #d4eeef;
  --color-primary-faint: rgba(14,122,128,0.08);
  --color-success: #3a7a1e;
  --color-success-bg: #e1f0d6;
  --color-error: #b52a4a;
  --color-error-bg: #f8dde3;
  --color-warning: #8a6b00;
  --color-warning-bg: #fef3d0;
  --color-gold: #c89500;
  --color-gold-bg: #fef6d8;
  --shadow-sm: 0 1px 3px rgba(30,29,26,0.06);
  --shadow-md: 0 4px 12px rgba(30,29,26,0.08);
  --shadow-lg: 0 12px 32px rgba(30,29,26,0.12);
  --radius-sm: 6px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --radius-xl: 16px;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Consolas', monospace;
  --sidebar-w: 300px;
  --header-h: 56px;
  --transition: 180ms cubic-bezier(0.16, 1, 0.3, 1);
}
[data-theme='dark'] {
  --color-bg: #1a1918;
  --color-surface: #222120;
  --color-surface-2: #2a2928;
  --color-surface-code: #2e2d2c;
  --color-border: #3a3938;
  --color-text: #d4d3d0;
  --color-text-muted: #8a8986;
  --color-text-faint: #5e5d5a;
  --color-primary: #4fa8ae;
  --color-primary-hover: #3cc0c8;
  --color-primary-bg: rgba(79,168,174,0.12);
  --color-primary-faint: rgba(79,168,174,0.06);
  --color-success: #6aaa42;
  --color-success-bg: rgba(106,170,66,0.12);
  --color-error: #e06080;
  --color-error-bg: rgba(224,96,128,0.12);
  --color-warning: #d4a800;
  --color-warning-bg: rgba(212,168,0,0.12);
  --color-gold: #e8b800;
  --color-gold-bg: rgba(232,184,0,0.12);
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.2);
  --shadow-md: 0 4px 12px rgba(0,0,0,0.3);
  --shadow-lg: 0 12px 32px rgba(0,0,0,0.4);
}
@media (prefers-color-scheme: light) {
  :root:not([data-theme]) {
    --color-bg: #f5f4f0; --color-surface: #edecea; --color-surface-2: #e4e3df;
    --color-surface-code: #dddcd8; --color-border: #c8c6c0; --color-text: #1e1d1a;
    --color-text-muted: #6b6a66; --color-text-faint: #9e9d99; --color-primary: #0e7a80;
    --color-primary-hover: #0a5c61; --color-primary-bg: #d4eeef;
    --color-primary-faint: rgba(14,122,128,0.08);
    --color-success: #3a7a1e; --color-success-bg: #e1f0d6;
    --color-error: #b52a4a; --color-error-bg: #f8dde3;
    --color-warning: #8a6b00; --color-warning-bg: #fef3d0;
    --color-gold: #c89500; --color-gold-bg: #fef6d8;
    --shadow-sm: 0 1px 3px rgba(30,29,26,0.06); --shadow-md: 0 4px 12px rgba(30,29,26,0.08);
  }
}

/* === SR-ONLY === */
.sr-only, .focus-visible-skip {
  position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0,0,0,0); white-space: nowrap; border: 0;
}
.focus-visible-skip:focus {
  position: fixed; top: 8px; left: 8px; width: auto; height: auto;
  clip: auto; padding: 8px 16px; background: var(--color-primary);
  color: #fff; z-index: 9999; border-radius: var(--radius-sm);
}

/* === HEADER === */
.header {
  position: fixed; top: 0; left: 0; right: 0; z-index: 100;
  height: var(--header-h); display: flex; align-items: center;
  justify-content: space-between; padding: 0 16px; gap: 12px;
  background: var(--color-surface); border-bottom: 1px solid var(--color-border);
  backdrop-filter: blur(12px);
}
.header-left { display: flex; align-items: center; gap: 12px; flex-shrink: 0; }
.header-center { flex: 1; display: flex; justify-content: center; max-width: 400px; margin: 0 auto; }
.header-right { display: flex; align-items: center; gap: 12px; flex-shrink: 0; }

.sidebar-toggle { display: none; padding: 6px; border-radius: var(--radius-sm); color: var(--color-text-muted); }
.sidebar-toggle:hover { background: var(--color-surface-2); color: var(--color-text); }

.logo { display: flex; align-items: center; gap: 8px; color: var(--color-text); }
.logo-text { font-weight: 700; font-size: 18px; letter-spacing: -0.02em; white-space: nowrap; }

.search-trigger {
  display: flex; align-items: center; gap: 8px; padding: 6px 14px;
  background: var(--color-bg); border: 1px solid var(--color-border);
  border-radius: var(--radius-lg); font-size: 14px; color: var(--color-text-faint);
  width: 100%; max-width: 360px; transition: border-color var(--transition);
}
.search-trigger:hover { border-color: var(--color-primary); }
.search-trigger kbd {
  margin-left: auto; padding: 2px 6px; background: var(--color-surface-2);
  border-radius: 4px; font-size: 11px; font-family: var(--font-mono);
  color: var(--color-text-muted); border: 1px solid var(--color-border);
}

.xp-display {
  display: flex; align-items: center; gap: 6px; padding: 4px 10px;
  background: var(--color-primary-faint); border-radius: var(--radius-lg);
  font-size: 13px; font-weight: 600; color: var(--color-primary);
  white-space: nowrap;
}
.level-display {
  display: flex; align-items: center; gap: 6px; font-size: 13px;
  color: var(--color-text-muted); white-space: nowrap;
}
.level-badge {
  padding: 2px 8px; background: var(--color-gold-bg); color: var(--color-gold);
  border-radius: var(--radius-sm); font-weight: 700; font-size: 12px;
}
.theme-toggle {
  padding: 6px; border-radius: var(--radius-sm); color: var(--color-text-muted);
  transition: color var(--transition), background var(--transition);
}
.theme-toggle:hover { background: var(--color-surface-2); color: var(--color-text); }

/* === LAYOUT === */
.layout {
  display: flex; margin-top: var(--header-h); min-height: calc(100dvh - var(--header-h));
}

/* === SIDEBAR === */
.sidebar {
  position: fixed; top: var(--header-h); left: 0; bottom: 0;
  width: var(--sidebar-w); background: var(--color-surface);
  border-right: 1px solid var(--color-border); overflow-y: auto;
  z-index: 50; transition: transform 0.3s ease;
}
.sidebar-inner { padding: 16px; }

.overall-progress { margin-bottom: 20px; }
.progress-header {
  display: flex; justify-content: space-between; font-size: 13px;
  font-weight: 600; margin-bottom: 6px; color: var(--color-text-muted);
}
.progress-bar {
  height: 6px; background: var(--color-surface-2); border-radius: 3px; overflow: hidden;
}
.progress-fill {
  height: 100%; background: var(--color-primary); border-radius: 3px;
  transition: width 0.5s ease;
}

/* Track Nav */
.track-group { margin-bottom: 4px; }
.track-header {
  display: flex; align-items: center; gap: 8px; padding: 8px 10px;
  border-radius: var(--radius-md); font-size: 13px; font-weight: 600;
  color: var(--color-text); cursor: pointer; width: 100%;
  transition: background var(--transition);
}
.track-header:hover { background: var(--color-surface-2); }
.track-header.active { background: var(--color-primary-faint); color: var(--color-primary); }
.track-icon-sm { font-size: 16px; flex-shrink: 0; width: 24px; text-align: center; }
.track-label { flex: 1; text-align: left; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.track-progress-mini {
  width: 32px; height: 4px; background: var(--color-surface-2); border-radius: 2px;
  overflow: hidden; flex-shrink: 0;
}
.track-progress-mini-fill { height: 100%; background: var(--color-primary); border-radius: 2px; transition: width 0.3s ease; }
.track-chevron {
  transition: transform 0.2s ease; color: var(--color-text-faint); flex-shrink: 0;
}
.track-chevron.open { transform: rotate(90deg); }
.track-lessons { padding-left: 36px; overflow: hidden; max-height: 0; transition: max-height 0.3s ease; }
.track-lessons.open { max-height: 2000px; }
.lesson-link {
  display: flex; align-items: center; gap: 8px; padding: 5px 10px;
  font-size: 13px; color: var(--color-text-muted); border-radius: var(--radius-sm);
  cursor: pointer; transition: all var(--transition); width: 100%; text-align: left;
}
.lesson-link:hover { background: var(--color-surface-2); color: var(--color-text); }
.lesson-link.active { background: var(--color-primary-faint); color: var(--color-primary); font-weight: 500; }
.lesson-link.completed { color: var(--color-success); }
.lesson-check {
  width: 16px; height: 16px; border-radius: 50%; border: 2px solid var(--color-border);
  flex-shrink: 0; display: flex; align-items: center; justify-content: center;
  font-size: 10px; transition: all var(--transition);
}
.lesson-link.completed .lesson-check {
  background: var(--color-success); border-color: var(--color-success); color: #fff;
}
.quiz-link {
  display: flex; align-items: center; gap: 8px; padding: 5px 10px;
  font-size: 13px; color: var(--color-gold); border-radius: var(--radius-sm);
  cursor: pointer; width: 100%; text-align: left; font-weight: 500;
  transition: background var(--transition);
}
.quiz-link:hover { background: var(--color-gold-bg); }
.quiz-link.completed { color: var(--color-success); }

/* Achievements */
.achievements-section { margin-top: 24px; padding-top: 16px; border-top: 1px solid var(--color-border); }
.achievements-section h3 { font-size: 13px; font-weight: 600; color: var(--color-text-muted); margin-bottom: 10px; }
.achievements-grid { display: grid; grid-template-columns: repeat(5, 1fr); gap: 6px; }
.achievement-icon {
  width: 100%; aspect-ratio: 1; display: flex; align-items: center; justify-content: center;
  background: var(--color-surface-2); border-radius: var(--radius-md); font-size: 20px;
  opacity: 0.3; transition: all var(--transition); cursor: default;
  position: relative;
}
.achievement-icon.unlocked { opacity: 1; background: var(--color-gold-bg); }
.achievement-icon[title]::after { content: none; }

/* === MAIN CONTENT === */
.main-content {
  flex: 1; margin-left: var(--sidebar-w); padding: 32px clamp(20px, 4vw, 48px);
  max-width: 900px;
}

/* === WELCOME SCREEN === */
.welcome-screen { display: flex; align-items: center; justify-content: center; min-height: calc(100dvh - var(--header-h) - 64px); }
.welcome-hero { text-align: center; max-width: 640px; }
.welcome-hero h1 {
  font-size: clamp(2.5rem, 1rem + 5vw, 4rem); font-weight: 700;
  letter-spacing: -0.03em; margin-bottom: 8px;
  background: linear-gradient(135deg, var(--color-primary), var(--color-text));
  -webkit-background-clip: text; -webkit-text-fill-color: transparent;
  background-clip: text;
}
.welcome-subtitle { font-size: clamp(1.1rem, 0.9rem + 0.5vw, 1.35rem); color: var(--color-text-muted); margin-bottom: 16px; }
.welcome-desc { font-size: 15px; color: var(--color-text-muted); line-height: 1.7; margin-bottom: 32px; }
.welcome-tracks {
  display: grid; grid-template-columns: repeat(auto-fill, minmax(220px, 1fr)); gap: 10px;
  margin-bottom: 32px; text-align: left;
}
.welcome-track {
  display: flex; align-items: center; gap: 10px; padding: 12px 14px;
  background: var(--color-surface); border: 1px solid var(--color-border);
  border-radius: var(--radius-md); font-size: 14px; cursor: pointer;
  transition: all var(--transition);
}
.welcome-track:hover { border-color: var(--color-primary); background: var(--color-primary-faint); }
.track-icon { font-size: 20px; }

/* === BUTTONS === */
.btn-primary {
  padding: 10px 24px; background: var(--color-primary); color: #fff;
  border-radius: var(--radius-md); font-weight: 600; font-size: 15px;
  transition: background var(--transition), transform 0.1s;
  display: inline-flex; align-items: center; gap: 8px;
}
.btn-primary:hover { background: var(--color-primary-hover); }
.btn-primary:active { transform: scale(0.98); }
.btn-primary.btn-lg { padding: 14px 32px; font-size: 16px; border-radius: var(--radius-lg); }
.btn-secondary {
  padding: 10px 20px; background: var(--color-surface-2); color: var(--color-text);
  border-radius: var(--radius-md); font-weight: 500; font-size: 14px;
  border: 1px solid var(--color-border); transition: all var(--transition);
}
.btn-secondary:hover { border-color: var(--color-primary); color: var(--color-primary); }

/* === LESSON VIEW === */
.lesson-view { animation: fadeIn 0.3s ease; }
.lesson-header { margin-bottom: 24px; }
.breadcrumb { font-size: 13px; color: var(--color-text-faint); margin-bottom: 4px; }
.breadcrumb a { color: var(--color-primary); }
.lesson-header h2 { font-size: clamp(1.5rem, 1.2rem + 1vw, 2rem); font-weight: 700; letter-spacing: -0.02em; }

/* Lesson Body Content */
.lesson-body h3 {
  font-size: 18px; font-weight: 700; margin-top: 32px; margin-bottom: 12px;
  padding-bottom: 6px; border-bottom: 1px solid var(--color-border);
}
.lesson-body h4 { font-size: 16px; font-weight: 600; margin-top: 24px; margin-bottom: 8px; }
.lesson-body p { margin-bottom: 14px; color: var(--color-text); line-height: 1.7; font-size: 15px; }
.lesson-body ul, .lesson-body ol { margin-bottom: 14px; padding-left: 24px; }
.lesson-body li { margin-bottom: 6px; font-size: 15px; line-height: 1.6; }
.lesson-body strong { font-weight: 600; }
.lesson-body em { font-style: italic; color: var(--color-text-muted); }
.lesson-body a { color: var(--color-primary); }

/* Code Blocks */
.code-block-wrap {
  position: relative; margin: 16px 0; border-radius: var(--radius-md);
  background: var(--color-surface-code); border: 1px solid var(--color-border);
  overflow: hidden;
}
.code-block-header {
  display: flex; align-items: center; justify-content: space-between;
  padding: 6px 12px; background: var(--color-surface-2);
  border-bottom: 1px solid var(--color-border); font-size: 12px;
  font-family: var(--font-mono); color: var(--color-text-faint);
}
.copy-btn {
  padding: 3px 10px; font-size: 12px; color: var(--color-text-muted);
  background: var(--color-surface); border: 1px solid var(--color-border);
  border-radius: 4px; font-family: var(--font-mono);
  transition: all var(--transition);
}
.copy-btn:hover { color: var(--color-primary); border-color: var(--color-primary); }
.copy-btn.copied { color: var(--color-success); border-color: var(--color-success); }
.code-block-wrap pre {
  padding: 14px 16px; overflow-x: auto; font-size: 13.5px; line-height: 1.55;
  font-family: var(--font-mono); color: var(--color-text);
  -webkit-overflow-scrolling: touch;
}
.code-block-wrap code { font-family: inherit; }

/* Inline code */
.lesson-body code:not(pre code) {
  padding: 2px 7px; background: var(--color-surface-code);
  border-radius: 4px; font-family: var(--font-mono); font-size: 13.5px;
  border: 1px solid var(--color-border); color: var(--color-primary);
}

/* Info/Tip/Warning boxes */
.info-box {
  padding: 14px 16px; margin: 16px 0; border-radius: var(--radius-md);
  border-left: 4px solid; font-size: 14px; line-height: 1.6;
}
.info-box.tip { border-color: var(--color-primary); background: var(--color-primary-faint); }
.info-box.warning { border-color: var(--color-warning); background: var(--color-warning-bg); }
.info-box.error { border-color: var(--color-error); background: var(--color-error-bg); }
.info-box.success { border-color: var(--color-success); background: var(--color-success-bg); }
.info-box-title { font-weight: 700; margin-bottom: 4px; display: flex; align-items: center; gap: 6px; }

/* Tables in lessons */
.lesson-table {
  width: 100%; border-collapse: collapse; margin: 16px 0;
  font-size: 14px; overflow-x: auto; display: block;
}
.lesson-table th, .lesson-table td {
  padding: 10px 14px; text-align: left; border: 1px solid var(--color-border);
}
.lesson-table th {
  background: var(--color-surface-2); font-weight: 600;
  font-size: 13px; color: var(--color-text-muted); white-space: nowrap;
}
.lesson-table td { background: var(--color-surface); }

/* Lesson Footer */
.lesson-footer {
  display: flex; justify-content: space-between; align-items: center;
  margin-top: 40px; padding-top: 20px; border-top: 1px solid var(--color-border);
  gap: 12px;
}

/* === QUIZ VIEW === */
.quiz-view { animation: fadeIn 0.3s ease; max-width: 700px; }
.quiz-header { margin-bottom: 24px; }
.quiz-header h2 { font-size: 22px; font-weight: 700; margin-bottom: 8px; }
.quiz-progress { font-size: 14px; color: var(--color-text-muted); }
.quiz-body { margin-bottom: 24px; }
.quiz-question { font-size: 16px; font-weight: 600; margin-bottom: 16px; line-height: 1.5; }
.quiz-question code {
  padding: 2px 7px; background: var(--color-surface-code);
  border-radius: 4px; font-family: var(--font-mono); font-size: 14px;
  border: 1px solid var(--color-border);
}
.quiz-options { display: flex; flex-direction: column; gap: 8px; }
.quiz-option {
  display: flex; align-items: flex-start; gap: 12px; padding: 14px 16px;
  background: var(--color-surface); border: 2px solid var(--color-border);
  border-radius: var(--radius-md); cursor: pointer; font-size: 15px;
  transition: all var(--transition); line-height: 1.5; width: 100%; text-align: left;
}
.quiz-option:hover { border-color: var(--color-primary); background: var(--color-primary-faint); }
.quiz-option.selected { border-color: var(--color-primary); background: var(--color-primary-faint); }
.quiz-option.correct { border-color: var(--color-success); background: var(--color-success-bg); }
.quiz-option.wrong { border-color: var(--color-error); background: var(--color-error-bg); }
.quiz-option-marker {
  width: 22px; height: 22px; border-radius: 50%; border: 2px solid var(--color-border);
  flex-shrink: 0; display: flex; align-items: center; justify-content: center;
  font-size: 12px; font-weight: 700; margin-top: 1px;
  transition: all var(--transition);
}
.quiz-option.selected .quiz-option-marker { border-color: var(--color-primary); background: var(--color-primary); color: #fff; }
.quiz-option.correct .quiz-option-marker { border-color: var(--color-success); background: var(--color-success); color: #fff; }
.quiz-option.wrong .quiz-option-marker { border-color: var(--color-error); background: var(--color-error); color: #fff; }
.quiz-explanation {
  margin-top: 16px; padding: 14px 16px; border-radius: var(--radius-md);
  font-size: 14px; line-height: 1.6; display: none;
}
.quiz-explanation.show { display: block; }
.quiz-explanation.correct-exp { background: var(--color-success-bg); border-left: 4px solid var(--color-success); }
.quiz-explanation.wrong-exp { background: var(--color-error-bg); border-left: 4px solid var(--color-error); }
.quiz-footer { display: flex; gap: 12px; }

/* === SEARCH OVERLAY === */
.search-overlay {
  position: fixed; inset: 0; z-index: 200; background: rgba(0,0,0,0.5);
  display: flex; align-items: flex-start; justify-content: center;
  padding-top: min(20vh, 160px); backdrop-filter: blur(4px);
  animation: fadeIn 0.15s ease;
}
.search-overlay[hidden] { display: none; }
.search-modal {
  width: min(560px, 90vw); background: var(--color-surface);
  border: 1px solid var(--color-border); border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg); overflow: hidden;
}
.search-input-wrap {
  display: flex; align-items: center; gap: 10px; padding: 14px 16px;
  border-bottom: 1px solid var(--color-border);
}
.search-input-wrap svg { flex-shrink: 0; color: var(--color-text-faint); }
.search-input-wrap input {
  flex: 1; border: none; background: none; outline: none;
  font-size: 16px; color: var(--color-text);
}
.search-input-wrap input::placeholder { color: var(--color-text-faint); }
.search-input-wrap kbd {
  padding: 2px 8px; background: var(--color-surface-2); border-radius: 4px;
  font-size: 12px; font-family: var(--font-mono); color: var(--color-text-muted);
  border: 1px solid var(--color-border);
}
.search-results { max-height: 360px; overflow-y: auto; }
.search-result-item {
  padding: 10px 16px; cursor: pointer; display: flex; flex-direction: column;
  gap: 2px; transition: background var(--transition);
}
.search-result-item:hover { background: var(--color-primary-faint); }
.search-result-track { font-size: 12px; color: var(--color-text-faint); }
.search-result-title { font-size: 14px; font-weight: 500; color: var(--color-text); }
.search-no-results { padding: 24px 16px; text-align: center; color: var(--color-text-faint); font-size: 14px; }

/* === LEVEL UP MODAL === */
.levelup-modal {
  position: fixed; inset: 0; z-index: 300; background: rgba(0,0,0,0.6);
  display: flex; align-items: center; justify-content: center;
  backdrop-filter: blur(6px); animation: fadeIn 0.3s ease;
}
.levelup-modal[hidden] { display: none; }
.levelup-content {
  text-align: center; padding: 48px 40px; background: var(--color-surface);
  border: 1px solid var(--color-border); border-radius: var(--radius-xl);
  box-shadow: var(--shadow-lg); max-width: 400px; width: 90%;
  animation: scaleIn 0.4s cubic-bezier(0.16, 1, 0.3, 1);
}
.levelup-badge { font-size: 64px; margin-bottom: 16px; }
.levelup-content h2 {
  font-size: 28px; font-weight: 700; margin-bottom: 8px;
  background: linear-gradient(135deg, var(--color-gold), var(--color-primary));
  -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text;
}
.levelup-content p { color: var(--color-text-muted); margin-bottom: 24px; font-size: 15px; }

/* === TOAST === */
.toast-container { position: fixed; top: 70px; right: 16px; z-index: 250; display: flex; flex-direction: column; gap: 8px; }
.toast {
  display: flex; align-items: center; gap: 10px; padding: 12px 18px;
  background: var(--color-surface); border: 1px solid var(--color-border);
  border-radius: var(--radius-md); box-shadow: var(--shadow-md);
  font-size: 14px; animation: slideInRight 0.4s ease, fadeOut 0.3s ease 3.5s forwards;
  min-width: 260px; max-width: 360px;
}
.toast-icon { font-size: 20px; flex-shrink: 0; }
.toast-text { flex: 1; }
.toast-title { font-weight: 600; font-size: 13px; }
.toast-desc { font-size: 12px; color: var(--color-text-muted); margin-top: 2px; }

/* === CONFETTI === */
#confetti-canvas {
  position: fixed; inset: 0; z-index: 400; pointer-events: none;
}

/* === ANIMATIONS === */
@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }
@keyframes fadeOut { from { opacity: 1; } to { opacity: 0; } }
@keyframes scaleIn { from { opacity: 0; transform: scale(0.85); } to { opacity: 1; transform: scale(1); } }
@keyframes slideInRight { from { opacity: 0; transform: translateX(60px); } to { opacity: 1; transform: translateX(0); } }

/* === RESPONSIVE === */
@media (max-width: 900px) {
  .sidebar-toggle { display: block; }
  .sidebar { transform: translateX(-100%); }
  .sidebar.open { transform: translateX(0); box-shadow: var(--shadow-lg); }
  .main-content { margin-left: 0; }
  .header-center { display: none; }
  .level-display span:not(.level-badge) { display: none; }
}
@media (max-width: 600px) {
  .welcome-tracks { grid-template-columns: 1fr; }
  .header { padding: 0 10px; gap: 8px; }
  .logo-text { font-size: 16px; }
  .xp-display span { font-size: 12px; }
  .lesson-body h3 { font-size: 17px; }
  .lesson-footer { flex-wrap: wrap; }
}