@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&display=swap');
  * { margin: 0; padding: 0; box-sizing: border-box; }
  body { font-family: 'Inter', system-ui, sans-serif; background: #f5f5f0; color: #d4d4d4; min-height: 100vh; display: flex; flex-direction: column; align-items: center; padding: 20px; letter-spacing: -0.01em; }
  h1 { font-size: 1.8rem; margin-bottom: 6px; color: #1a1a1a; font-weight: 300; letter-spacing: 0.04em; text-transform: uppercase; }
  h1 span { color: #c9a84c; font-weight: 600; }
  .subtitle { color: #666; margin-bottom: 8px; font-size: 0.9rem; font-weight: 400; letter-spacing: 0.02em; }
  .back-link { color: #888; text-decoration: none; font-size: 0.8rem; display: inline-block; margin-bottom: 20px; letter-spacing: 0.05em; text-transform: uppercase; font-weight: 500; transition: color 0.3s ease; }
  .back-link:hover { color: #c9a84c; }
  .container { display: flex; gap: 30px; flex-wrap: wrap; justify-content: center; max-width: 1100px; width: 100%; }
  .board-section { display: flex; flex-direction: column; align-items: center; }
  .board { display: grid; grid-template-columns: repeat(8, 1fr); width: 400px; height: 400px; border: 2px solid #333; border-radius: 2px; overflow: hidden; box-shadow: 0 4px 24px rgba(0,0,0,0.3); }
  .square { width: 50px; height: 50px; display: flex; align-items: center; justify-content: center; font-size: 36px; line-height: 1; user-select: none; position: relative; }
  .light { background: #e8dcc8; }
  .dark { background: #8b7355; }
  .highlight { box-shadow: inset 0 0 0 3px #c9a84c; }
  .last-move { background: #c9a84c !important; }
  .last-move.dark { background: #a8893a !important; }
  .piece-white { color: #ffffff; text-shadow: 0 0 2px #000, 0 0 2px #000, 1px 1px 1px #000; }
  .piece-black { color: #1a1a1a; text-shadow: 0 0 2px rgba(255,255,255,0.3); }
  .file-labels, .rank-labels { display: flex; }
  .file-labels { width: 400px; justify-content: space-around; padding: 4px 0; color: #888; font-size: 0.7rem; font-weight: 500; letter-spacing: 0.05em; }
  .rank-labels { flex-direction: column; justify-content: space-around; padding: 0 6px; color: #888; font-size: 0.7rem; height: 400px; font-weight: 500; letter-spacing: 0.05em; }
  .board-with-labels { display: flex; align-items: center; }

  .info-panel { flex: 1; min-width: 280px; max-width: 440px; }
  .step-card { background: #111; border-radius: 8px; padding: 22px; margin-bottom: 16px; border: 1px solid rgba(255,255,255,0.06); box-shadow:0 4px 20px rgba(0,0,0,0.15); }
  .step-number { display: inline-block; background: #c9a84c; color: #0a0a0a; border-radius: 50%; width: 28px; height: 28px; text-align: center; line-height: 28px; font-weight: 700; font-size: 0.85rem; margin-right: 8px; }
  .step-move { font-weight: 600; font-size: 1.1rem; color: #fff; }
  .step-explanation { margin-top: 12px; line-height: 1.7; color: #999; font-size: 0.9rem; }
  .principle-tag { display: inline-block; background: rgba(201,168,76,0.06); color: #c9a84c; padding: 3px 12px; border-radius: 20px; font-size: 0.75rem; margin-top: 10px; margin-right: 4px; border: 1px solid rgba(201,168,76,0.15); font-weight: 500; letter-spacing: 0.03em; }

  .controls { display: flex; gap: 8px; margin-top: 16px; margin-bottom: 10px; }
  .controls button { background: #1a1a1a; color: #999; border: 1px solid rgba(255,255,255,0.08); padding: 10px 18px; border-radius: 6px; cursor: pointer; font-size: 1rem; transition: all 0.3s ease; font-family: inherit; }
  .controls button:hover { background: rgba(255,255,255,0.06); color: #fff; border-color: rgba(255,255,255,0.15); }
  .controls button:disabled { opacity: 0.25; cursor: not-allowed; }
  .controls button:disabled:hover { background: #1a1a1a; border-color: rgba(255,255,255,0.08); color: #999; }

  .move-indicator { text-align: center; margin-top: 8px; color: #888; font-size: 0.8rem; letter-spacing: 0.03em; }
  .legend { display: flex; gap: 16px; margin-top: 8px; font-size: 0.75rem; color: #666; letter-spacing: 0.02em; }

  .tabs { display: flex; gap: 4px; margin-bottom: 16px; flex-wrap: wrap; justify-content: center; }
  .tab { background: transparent; color: #888; border: 1px solid transparent; padding: 10px 16px; border-radius: 6px 6px 0 0; cursor: pointer; font-size: 0.8rem; transition: all 0.3s ease; white-space: nowrap; font-family: inherit; font-weight: 500; letter-spacing: 0.02em; }
  .tab:hover { color: #1a1a1a; background: rgba(0,0,0,0.05); }
  .tab.active { color: #c9a84c; border-color: rgba(201,168,76,0.3); background: rgba(201,168,76,0.06); }

  .quiz-section { background: #111; border-radius: 8px; padding: 22px; border: 1px solid rgba(255,255,255,0.06); margin-top: 12px; box-shadow:0 4px 20px rgba(0,0,0,0.15); }
  .quiz-section h3 { color: #c9a84c; margin-bottom: 14px; font-size: 0.85rem; font-weight: 600; letter-spacing: 0.08em; text-transform: uppercase; }
  .quiz-btn { display: block; width: 100%; text-align: left; background: rgba(255,255,255,0.03); color: #bbb; border: 1px solid rgba(255,255,255,0.08); padding: 14px 18px; border-radius: 6px; cursor: pointer; font-size: 0.9rem; margin-bottom: 8px; transition: all 0.3s ease; font-family: inherit; }
  .quiz-btn:hover { border-color: rgba(201,168,76,0.3); background: rgba(201,168,76,0.06); color: #fff; }
  .quiz-btn.correct { background: rgba(90,158,111,0.12); border-color: rgba(90,158,111,0.3); color: #7cc494; }
  .quiz-btn.wrong { background: rgba(196,92,92,0.12); border-color: rgba(196,92,92,0.3); color: #d48a8a; }
  .quiz-feedback { margin-top: 14px; padding: 16px; border-radius: 8px; line-height: 1.7; font-size: 0.88rem; display: none; }
  .quiz-feedback.show { display: block; }
  .quiz-feedback.correct { background: rgba(90,158,111,0.1); color: #7cc494; border: 1px solid rgba(90,158,111,0.2); }
  .quiz-feedback.wrong { background: rgba(196,92,92,0.1); color: #d48a8a; border: 1px solid rgba(196,92,92,0.2); }

  .plan-card { background: rgba(201,168,76,0.04); border-radius: 8px; padding: 22px; margin-top: 16px; border: 1px solid rgba(201,168,76,0.12); }
  .plan-card h3 { color: #c9a84c; margin-bottom: 10px; font-size: 0.95rem; font-weight: 600; }
  .plan-card p { color: #999; line-height: 1.7; font-size: 0.88rem; margin-bottom: 6px; }

  ::-webkit-scrollbar { width: 6px; }
  ::-webkit-scrollbar-track { background: #eee; }
  ::-webkit-scrollbar-thumb { background: #bbb; border-radius: 3px; }
  ::-webkit-scrollbar-thumb:hover { background: #999; }

  @media (max-width: 700px) {
    body { padding: 16px; }
    h1 { font-size: 1.4rem; }
    .board { width: 320px; height: 320px; }
    .square { width: 40px; height: 40px; font-size: 28px; }
    .file-labels { width: 320px; }
    .rank-labels { height: 320px; }
    .tab { font-size: 0.7rem; padding: 8px 10px; }
  }