:root {
    --bg: #0f0e17;
    --surface: #1a1830;
    --card: #221f38;
    --accent1: #ff6b6b;
    --accent2: #ffd166;
    --accent3: #06d6a0;
    --accent4: #118ab2;
    --accent5: #c77dff;
    --text: #fffffe;
    --muted: #a7a9be;
    --code-bg: #13111f;
    --border: #2e2b4a;
  }

  * { box-sizing: border-box; margin: 0; padding: 0; }

  body {
    font-family: 'Nunito', sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.7;
    overflow-x: hidden;
  }

  /* HEADER */
  header {
    background: linear-gradient(135deg, #1a0533 0%, #0a1628 50%, #001a12 100%);
    padding: 60px 40px 80px;
    text-align: center;
    position: relative;
    overflow: hidden;
  }
  header::before {
    content: '';
    position: absolute; inset: 0;
    background: radial-gradient(circle at 30% 50%, rgba(199,125,255,0.15) 0%, transparent 60%),
                radial-gradient(circle at 70% 30%, rgba(6,214,160,0.12) 0%, transparent 50%);
  }
  .header-badge {
    display: inline-block;
    background: linear-gradient(90deg, var(--accent5), var(--accent3));
    color: var(--bg);
    font-weight: 800;
    font-size: 13px;
    letter-spacing: 2px;
    text-transform: uppercase;
    padding: 6px 18px;
    border-radius: 20px;
    margin-bottom: 20px;
  }
  header h1 {
    font-family: 'Fredoka One', cursive;
    font-size: clamp(2.4rem, 6vw, 4.5rem);
    background: linear-gradient(135deg, #fff 30%, var(--accent5) 70%, var(--accent3));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    line-height: 1.1;
    margin-bottom: 16px;
  }
  header p {
    font-size: 1.15rem;
    color: var(--muted);
    max-width: 560px;
    margin: 0 auto 32px;
  }
  .header-stars {
    font-size: 1.6rem;
    letter-spacing: 6px;
    opacity: 0.7;
  }

  /* PROGRESS BAR */
  .progress-bar-wrap {
    background: var(--surface);
    padding: 14px 40px;
    display: flex;
    align-items: center;
    gap: 16px;
    border-bottom: 1px solid var(--border);
    position: sticky;
    top: 0;
    z-index: 100;
  }
  .progress-label { font-size: 13px; font-weight: 700; color: var(--muted); white-space: nowrap; }
  .progress-track {
    flex: 1;
    height: 8px;
    background: var(--card);
    border-radius: 10px;
    overflow: hidden;
  }
  .progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--accent5), var(--accent3));
    border-radius: 10px;
    transition: width 0.5s ease;
    width: 0%;
  }
  .progress-pct { font-size: 13px; font-weight: 800; color: var(--accent3); }

  /* LAYOUT */
  .layout {
    display: flex;
    max-width: 1200px;
    margin: 0 auto;
    gap: 0;
  }

  /* SIDEBAR */
  .sidebar {
    width: 270px;
    flex-shrink: 0;
    padding: 30px 20px;
    position: sticky;
    top: 53px;
    height: calc(100vh - 53px);
    overflow-y: auto;
    border-right: 1px solid var(--border);
  }
  .sidebar-title {
    font-size: 11px;
    font-weight: 800;
    letter-spacing: 2px;
    text-transform: uppercase;
    color: var(--muted);
    margin-bottom: 16px;
    padding-left: 8px;
  }
  .nav-item {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 10px 12px;
    border-radius: 10px;
    cursor: pointer;
    transition: all 0.2s;
    margin-bottom: 4px;
    font-size: 14px;
    font-weight: 600;
    color: var(--muted);
    text-decoration: none;
  }
  .nav-item:hover { background: var(--card); color: var(--text); }
  .nav-item.active { background: var(--card); color: var(--text); border-left: 3px solid var(--accent5); }
  .nav-item .nav-icon { font-size: 18px; flex-shrink: 0; }
  .nav-item .nav-check { margin-left: auto; font-size: 14px; color: var(--accent3); }

  /* MAIN CONTENT */
  .main {
    flex: 1;
    padding: 40px 50px;
    min-width: 0;
  }

  /* LESSON SECTION */
  .lesson { display: none; animation: fadeIn 0.4s ease; }
  .lesson.active { display: block; }
  @keyframes fadeIn { from { opacity: 0; transform: translateY(12px); } to { opacity: 1; transform: translateY(0); } }

  .lesson-header {
    margin-bottom: 36px;
  }
  .lesson-num {
    font-size: 12px;
    font-weight: 800;
    letter-spacing: 2px;
    text-transform: uppercase;
    color: var(--accent5);
    margin-bottom: 8px;
  }
  .lesson h2 {
    font-family: 'Fredoka One', cursive;
    font-size: clamp(1.8rem, 3vw, 2.8rem);
    line-height: 1.15;
    margin-bottom: 12px;
  }
  .lesson-intro {
    font-size: 1.05rem;
    color: var(--muted);
    max-width: 680px;
    border-left: 3px solid var(--accent5);
    padding-left: 16px;
  }

  /* CARDS */
  .card {
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: 16px;
    padding: 28px;
    margin-bottom: 28px;
  }
  .card-title {
    font-family: 'Fredoka One', cursive;
    font-size: 1.25rem;
    margin-bottom: 14px;
    display: flex;
    align-items: center;
    gap: 10px;
  }
  .card p, .card li { font-size: 0.97rem; color: #d4d4e8; margin-bottom: 10px; }
  .card ul, .card ol { padding-left: 20px; }
  .card li { margin-bottom: 6px; }

  /* CALLOUT BOXES */
  .callout {
    border-radius: 14px;
    padding: 20px 24px;
    margin: 20px 0;
    display: flex;
    gap: 14px;
    align-items: flex-start;
  }
  .callout-emoji { font-size: 1.5rem; flex-shrink: 0; margin-top: 2px; }
  .callout-body { font-size: 0.95rem; }
  .callout-body strong { display: block; font-size: 1rem; margin-bottom: 4px; }
  .callout.tip { background: rgba(6,214,160,0.1); border: 1px solid rgba(6,214,160,0.25); }
  .callout.tip .callout-body strong { color: var(--accent3); }
  .callout.warn { background: rgba(255,209,102,0.1); border: 1px solid rgba(255,209,102,0.25); }
  .callout.warn .callout-body strong { color: var(--accent2); }
  .callout.fun { background: rgba(199,125,255,0.1); border: 1px solid rgba(199,125,255,0.25); }
  .callout.fun .callout-body strong { color: var(--accent5); }
  .callout.info { background: rgba(17,138,178,0.12); border: 1px solid rgba(17,138,178,0.3); }
  .callout.info .callout-body strong { color: #5bc4e8; }

  /* CODE BLOCKS */
  .code-block {
    background: var(--code-bg);
    border: 1px solid var(--border);
    border-radius: 12px;
    margin: 18px 0;
    overflow: hidden;
  }
  .code-header {
    background: #1c1929;
    padding: 10px 18px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    border-bottom: 1px solid var(--border);
  }
  .code-lang {
    font-size: 12px;
    font-weight: 700;
    color: var(--accent5);
    letter-spacing: 1px;
    text-transform: uppercase;
  }
  .code-dots { display: flex; gap: 6px; }
  .code-dots span {
    width: 10px; height: 10px; border-radius: 50%;
  }
  .code-dots span:nth-child(1) { background: #ff5f56; }
  .code-dots span:nth-child(2) { background: #ffbd2e; }
  .code-dots span:nth-child(3) { background: #27c93f; }
  pre {
    padding: 20px 22px;
    overflow-x: auto;
    font-family: 'Fira Code', monospace;
    font-size: 0.88rem;
    line-height: 1.8;
  }
  /* Syntax colors */
  .kw { color: #c77dff; font-weight: 500; }
  .cl { color: #ffd166; }
  .fn { color: #06d6a0; }
  .str { color: #ff9f6b; }
  .cm { color: #5a5880; font-style: italic; }
  .num { color: #ff6b9d; }
  .var { color: #e8e8f0; }

  /* QUIZ */
  .quiz-block {
    background: linear-gradient(135deg, #1a1830, #1e1535);
    border: 1px solid var(--accent5);
    border-radius: 16px;
    padding: 28px;
    margin: 28px 0;
  }
  .quiz-title {
    font-family: 'Fredoka One', cursive;
    font-size: 1.2rem;
    color: var(--accent5);
    margin-bottom: 14px;
    display: flex;
    align-items: center;
    gap: 8px;
  }
  .quiz-q { font-size: 1rem; font-weight: 700; margin-bottom: 16px; }
  .quiz-options { display: flex; flex-direction: column; gap: 10px; }
  .quiz-option {
    background: var(--card);
    border: 2px solid var(--border);
    border-radius: 10px;
    padding: 12px 18px;
    cursor: pointer;
    font-size: 0.95rem;
    font-weight: 600;
    transition: all 0.2s;
    text-align: left;
    color: var(--text);
  }
  .quiz-option:hover { border-color: var(--accent5); background: rgba(199,125,255,0.08); }
  .quiz-option.correct { border-color: var(--accent3); background: rgba(6,214,160,0.12); color: var(--accent3); }
  .quiz-option.wrong { border-color: var(--accent1); background: rgba(255,107,107,0.1); color: var(--accent1); }
  .quiz-feedback {
    margin-top: 14px;
    padding: 12px 16px;
    border-radius: 10px;
    font-weight: 700;
    font-size: 0.95rem;
    display: none;
  }
  .quiz-feedback.show { display: block; }
  .quiz-feedback.ok { background: rgba(6,214,160,0.15); color: var(--accent3); border: 1px solid var(--accent3); }
  .quiz-feedback.bad { background: rgba(255,107,107,0.1); color: var(--accent1); border: 1px solid var(--accent1); }

  /* ANALOGY BOXES */
  .analogy {
    background: linear-gradient(135deg, rgba(255,209,102,0.08), rgba(255,107,107,0.06));
    border: 1px solid rgba(255,209,102,0.2);
    border-radius: 14px;
    padding: 22px 26px;
    margin: 20px 0;
  }
  .analogy-label {
    font-size: 11px;
    font-weight: 800;
    letter-spacing: 2px;
    text-transform: uppercase;
    color: var(--accent2);
    margin-bottom: 8px;
  }
  .analogy p { font-size: 0.97rem; color: #ddd; }

  /* CHALLENGE BOX */
  .challenge {
    background: linear-gradient(135deg, rgba(17,138,178,0.12), rgba(6,214,160,0.08));
    border: 1px solid rgba(17,138,178,0.3);
    border-radius: 14px;
    padding: 24px 28px;
    margin: 24px 0;
  }
  .challenge-label {
    font-size: 11px;
    font-weight: 800;
    letter-spacing: 2px;
    text-transform: uppercase;
    color: #5bc4e8;
    margin-bottom: 8px;
  }
  .challenge h4 { font-size: 1.05rem; margin-bottom: 10px; }
  .challenge p, .challenge li { font-size: 0.95rem; color: #ccc; }

  /* NAV BUTTONS */
  .lesson-nav {
    display: flex;
    justify-content: space-between;
    margin-top: 50px;
    padding-top: 28px;
    border-top: 1px solid var(--border);
  }
  .btn {
    padding: 12px 28px;
    border-radius: 12px;
    font-family: 'Nunito', sans-serif;
    font-size: 0.95rem;
    font-weight: 800;
    cursor: pointer;
    border: none;
    transition: all 0.2s;
  }
  .btn-next {
    background: linear-gradient(135deg, var(--accent5), var(--accent4));
    color: white;
  }
  .btn-next:hover { transform: translateY(-2px); box-shadow: 0 8px 24px rgba(199,125,255,0.3); }
  .btn-prev {
    background: var(--card);
    color: var(--muted);
    border: 1px solid var(--border);
  }
  .btn-prev:hover { color: var(--text); border-color: var(--accent5); }
  .btn:disabled { opacity: 0.3; cursor: not-allowed; transform: none !important; box-shadow: none !important; }

  /* DIVIDER */
  .section-divider {
    display: flex;
    align-items: center;
    gap: 14px;
    margin: 28px 0;
  }
  .section-divider span { font-size: 11px; font-weight: 800; letter-spacing: 2px; text-transform: uppercase; color: var(--muted); white-space: nowrap; }
  .section-divider::before, .section-divider::after { content: ''; flex: 1; height: 1px; background: var(--border); }

  /* TABLE */
  table { width: 100%; border-collapse: collapse; font-size: 0.92rem; margin: 16px 0; }
  th { background: var(--surface); color: var(--accent5); font-weight: 800; padding: 12px 16px; text-align: left; border-bottom: 2px solid var(--border); }
  td { padding: 11px 16px; border-bottom: 1px solid var(--border); color: #d4d4e8; }
  tr:hover td { background: rgba(255,255,255,0.02); }

  /* BADGE */
  .badge {
    display: inline-block;
    padding: 3px 10px;
    border-radius: 20px;
    font-size: 11px;
    font-weight: 800;
    letter-spacing: 0.5px;
  }
  .badge-green { background: rgba(6,214,160,0.15); color: var(--accent3); }
  .badge-purple { background: rgba(199,125,255,0.15); color: var(--accent5); }
  .badge-yellow { background: rgba(255,209,102,0.15); color: var(--accent2); }
  .badge-red { background: rgba(255,107,107,0.15); color: var(--accent1); }

  /* PILLAR CARDS (for 4 pillars) */
  .pillars {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 16px;
    margin: 24px 0;
  }
  .pillar-card {
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: 14px;
    padding: 22px;
    text-align: center;
    transition: transform 0.2s;
  }
  .pillar-card:hover { transform: translateY(-4px); }
  .pillar-icon { font-size: 2.5rem; margin-bottom: 12px; }
  .pillar-card h4 { font-family: 'Fredoka One', cursive; font-size: 1.1rem; margin-bottom: 8px; }
  .pillar-card p { font-size: 0.88rem; color: var(--muted); }

  /* SCROLLBAR */
  ::-webkit-scrollbar { width: 6px; height: 6px; }
  ::-webkit-scrollbar-track { background: transparent; }
  ::-webkit-scrollbar-thumb { background: var(--border); border-radius: 3px; }

  /* MOBILE */
  @media (max-width: 768px) {
    .sidebar { display: none; }
    .main { padding: 24px 20px; }
    .progress-bar-wrap { padding: 10px 20px; }
    header { padding: 40px 20px 60px; }
  }