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

    :root {
      --bg:      #0d1117;
      --surface: #161b22;
      --card:    #1c2128;
      --border:  #30363d;
      --accent:  #f7df1e;   /* JS yellow */
      --green:   #3fb950;
      --red:     #f85149;
      --blue:    #58a6ff;
      --text:    #e6edf3;
      --muted:   #8b949e;
      --radius:  12px;
    }

    html { scroll-behavior: smooth; }

    body {
      font-family: 'Outfit', sans-serif;
      background: var(--bg);
      color: var(--text);
      min-height: 100vh;
    }

    /* ── NAVBAR ─────────────────────────────────── */
    nav {
      background: rgba(13,17,23,0.9);
      backdrop-filter: blur(12px);
      border-bottom: 1px solid var(--border);
      padding: 0 32px;
      height: 56px;
      display: flex;
      align-items: center;
      justify-content: space-between;
      position: sticky;
      top: 0;
      z-index: 100;
    }

    .nav-logo {
      font-family: 'Space Mono', monospace;
      font-size: 0.85rem;
      color: var(--text);
    }

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

    .nav-pills {
      display: flex;
      gap: 6px;
    }

    .nav-pills a {
      font-size: 0.75rem;
      color: var(--muted);
      text-decoration: none;
      padding: 4px 12px;
      border-radius: 20px;
      border: 1px solid transparent;
      transition: all 0.2s;
    }

    .nav-pills a:hover {
      color: var(--accent);
      border-color: rgba(247,223,30,0.3);
      background: rgba(247,223,30,0.06);
    }

    /* ── LAYOUT ─────────────────────────────────── */
    main {
      max-width: 860px;
      margin: 0 auto;
      padding: 48px 24px 80px;
      display: flex;
      flex-direction: column;
      gap: 32px;
    }

    .page-title {
      text-align: center;
      margin-bottom: 8px;
    }

    .page-title .tag {
      font-family: 'Space Mono', monospace;
      font-size: 0.68rem;
      color: var(--accent);
      letter-spacing: 0.2em;
      text-transform: uppercase;
      display: block;
      margin-bottom: 10px;
    }

    .page-title h1 {
      font-size: clamp(1.6rem, 4vw, 2.2rem);
      font-weight: 700;
      color: var(--text);
    }

    .page-title p {
      font-size: 0.9rem;
      color: var(--muted);
      margin-top: 8px;
    }

    /* ── EXERCISE CARD ───────────────────────────── */
    .ex-card {
      background: var(--card);
      border: 1px solid var(--border);
      border-radius: var(--radius);
      overflow: hidden;
      transition: border-color 0.25s;
    }

    .ex-card:hover { border-color: rgba(247,223,30,0.3); }

    .ex-header {
      display: flex;
      align-items: center;
      gap: 14px;
      padding: 20px 24px 16px;
      border-bottom: 1px solid var(--border);
    }

    .ex-num {
      font-family: 'Space Mono', monospace;
      font-size: 0.65rem;
      color: var(--accent);
      background: rgba(247,223,30,0.08);
      border: 1px solid rgba(247,223,30,0.2);
      padding: 3px 10px;
      border-radius: 20px;
      letter-spacing: 0.1em;
      white-space: nowrap;
    }

    .ex-header h2 {
      font-size: 1rem;
      font-weight: 600;
      color: var(--text);
    }

    .ex-body { padding: 24px; }

    /* ── FORM ELEMENTS ───────────────────────────── */
    .field { margin-bottom: 16px; }

    label {
      display: block;
      font-size: 0.78rem;
      font-weight: 600;
      color: var(--muted);
      margin-bottom: 6px;
      text-transform: uppercase;
      letter-spacing: 0.06em;
    }

    input[type="number"],
    input[type="text"],
    select {
      width: 100%;
      background: var(--surface);
      border: 1px solid var(--border);
      border-radius: 8px;
      color: var(--text);
      font-family: 'Outfit', sans-serif;
      font-size: 0.9rem;
      padding: 10px 14px;
      outline: none;
      transition: border-color 0.2s, box-shadow 0.2s;
    }

    input:focus, select:focus {
      border-color: var(--accent);
      box-shadow: 0 0 0 3px rgba(247,223,30,0.08);
    }

    input.error { border-color: var(--red) !important; box-shadow: 0 0 0 3px rgba(248,81,73,0.1); }
    input.ok    { border-color: var(--green) !important; }

    .err-msg {
      font-size: 0.75rem;
      color: var(--red);
      margin-top: 5px;
      min-height: 16px;
      display: block;
    }

    /* Row of inputs */
    .row { display: flex; gap: 12px; }
    .row .field { flex: 1; }

    /* ── BUTTON ──────────────────────────────────── */
    .btn {
      display: inline-flex;
      align-items: center;
      gap: 8px;
      padding: 10px 24px;
      border-radius: 8px;
      font-family: 'Outfit', sans-serif;
      font-size: 0.88rem;
      font-weight: 600;
      cursor: pointer;
      border: none;
      transition: all 0.2s;
    }

    .btn-yellow {
      background: var(--accent);
      color: #111;
    }

    .btn-yellow:hover {
      filter: brightness(1.1);
      transform: translateY(-1px);
    }

    .btn-ghost {
      background: transparent;
      color: var(--muted);
      border: 1px solid var(--border);
    }

    .btn-ghost:hover {
      color: var(--text);
      border-color: var(--muted);
    }

    .btn-row {
      display: flex;
      gap: 10px;
      margin-top: 4px;
    }

    /* ── OUTPUT BOX ──────────────────────────────── */
    .output {
      margin-top: 20px;
      background: var(--surface);
      border: 1px solid var(--border);
      border-radius: 8px;
      padding: 16px 20px;
      font-family: 'Space Mono', monospace;
      font-size: 0.82rem;
      line-height: 1.7;
      min-height: 52px;
      display: none;
    }

    .output.show { display: block; }

    .output.success { border-color: var(--green); color: var(--green); }
    .output.danger  { border-color: var(--red);   color: var(--red);   }
    .output.info    { border-color: var(--blue);  color: var(--blue);  }
    .output.neutral { border-color: var(--border);color: var(--text);  }

    .output-line { display: block; }
    .out-label   { color: var(--muted); font-size: 0.72rem; margin-bottom: 4px; display: block; }

    /* ── GUESS GAME ──────────────────────────────── */
    .guess-state {
      display: flex;
      gap: 12px;
      margin-bottom: 16px;
    }

    .state-pill {
      font-family: 'Space Mono', monospace;
      font-size: 0.7rem;
      padding: 4px 12px;
      border-radius: 20px;
      border: 1px solid var(--border);
      color: var(--muted);
    }

    .state-pill.active { border-color: var(--green); color: var(--green); background: rgba(63,185,80,0.08); }

    /* ── PATTERN OUTPUT ──────────────────────────── */
    .pattern-box {
      font-family: 'Space Mono', monospace;
      font-size: 1rem;
      line-height: 1.5;
      letter-spacing: 2px;
      color: var(--accent);
    }

    /* ── TABLE ───────────────────────────────────── */
    .mult-table {
      border-collapse: collapse;
      width: 100%;
      font-family: 'Space Mono', monospace;
      font-size: 0.72rem;
    }

    .mult-table td {
      padding: 5px 8px;
      text-align: right;
      border: 1px solid var(--border);
      color: var(--text);
      min-width: 36px;
    }

    .mult-table td.header-cell {
      background: rgba(247,223,30,0.08);
      color: var(--accent);
      font-weight: 700;
    }

    .mult-table td.diag {
      background: rgba(247,223,30,0.05);
      color: var(--accent);
    }

    /* ── ARRAY SECTION ───────────────────────────── */
    .array-display {
      display: flex;
      flex-wrap: wrap;
      gap: 6px;
      margin-bottom: 16px;
    }

    .num-badge {
      font-family: 'Space Mono', monospace;
      font-size: 0.75rem;
      padding: 4px 10px;
      border-radius: 6px;
      border: 1px solid var(--border);
    }

    .num-badge.pos { border-color: var(--green); color: var(--green); background: rgba(63,185,80,0.08); }
    .num-badge.neg { border-color: var(--red);   color: var(--red);   background: rgba(248,81,73,0.08); }
    .num-badge.zer { border-color: var(--muted); color: var(--muted); background: rgba(139,148,158,0.08); }