:root{font-family:system-ui,Avenir,Helvetica,Arial,sans-serif;line-height:1.5;font-weight:400;color-scheme:light dark;color:#ffffffde;background-color:#242424;font-synthesis:none;text-rendering:optimizeLegibility;-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale}a{font-weight:500;color:#646cff;text-decoration:inherit}a:hover{color:#535bf2}body{margin:0;display:flex;place-items:center;min-width:320px;min-height:100vh}h1{font-size:3.2em;line-height:1.1}button{border-radius:8px;border:1px solid transparent;padding:.6em 1.2em;font-size:1em;font-weight:500;font-family:inherit;background-color:#1a1a1a;cursor:pointer;transition:border-color .25s}button:hover{border-color:#646cff}button:focus,button:focus-visible{outline:4px auto -webkit-focus-ring-color}@media(prefers-color-scheme:light){:root{color:#213547;background-color:#fff}a:hover{color:#747bff}button{background-color:#f9f9f9}}.flashcard{background-color:transparent;width:100%;max-width:340px;height:460px;perspective:1000px;cursor:pointer;margin:0 auto}.flashcard-inner{position:relative;width:100%;height:100%;text-align:center;transition:transform .6s cubic-bezier(.4,0,.2,1);transform-style:preserve-3d;box-shadow:0 10px 30px -5px #0000001a;border-radius:24px}.flashcard.flipped .flashcard-inner{transform:rotateY(180deg)}.flashcard-front,.flashcard-back{position:absolute;width:100%;height:100%;-webkit-backface-visibility:hidden;backface-visibility:hidden;border-radius:24px;display:flex;flex-direction:column;justify-content:center;align-items:center;padding:30px;box-sizing:border-box}.flashcard-front{background:#fff;color:#1a1a1a;border:1px solid rgba(0,0,0,.05)}.flashcard-back{background:linear-gradient(135deg,#4f46e5,#7c3aed);color:#fff;transform:rotateY(180deg)}.card-content{display:flex;flex-direction:column;align-items:center;justify-content:center;height:100%;width:100%}.card-id{position:absolute;top:24px;left:24px;font-size:1rem;font-weight:600;opacity:.4}.card-text{font-size:3.5rem;margin:0;font-weight:700;line-height:1.2}.card-pinyin-large{font-size:2.5rem;font-family:Inter,sans-serif;font-weight:600;margin-bottom:16px}.card-text-masked{font-size:2.5rem;margin:10px 0 0;font-weight:500;color:#4b5563}.card-pinyin{font-size:2.2rem;margin-top:24px;font-weight:500;font-family:Inter,sans-serif}.instruction{position:absolute;bottom:30px;font-size:.85rem;opacity:.4;text-transform:uppercase;letter-spacing:1.5px;font-weight:600}.app-container{min-height:100vh;display:flex;flex-direction:column;align-items:center;background-color:#f8fafc;font-family:Inter,system-ui,-apple-system,sans-serif;padding:40px 20px;box-sizing:border-box}.header{text-align:center;margin-bottom:60px}.header h1{font-size:2.5rem;color:#1e293b;margin:0 0 12px;font-weight:800;letter-spacing:-.02em}.header p{color:#64748b;font-size:1.1rem;margin:0}.main-content{width:100%;max-width:800px;display:flex;flex-direction:column;align-items:center;gap:40px}.controls{display:flex;align-items:center;justify-content:space-between;width:100%;max-width:500px;gap:20px;margin-top:20px;background:#fff;padding:10px 20px;border-radius:20px;box-shadow:0 4px 6px -1px #0000001a,0 2px 4px -1px #0000000f}.center-controls{display:flex;align-items:center;gap:15px}.nav-btn{background:transparent;border:none;padding:12px 24px;border-radius:12px;font-size:1rem;font-weight:600;color:#475569;cursor:pointer;transition:all .2s}.nav-btn:hover:not(:disabled){background:#f1f5f9;color:#0f172a}.nav-btn:disabled{opacity:.3;cursor:not-allowed}.shuffle-btn{background:#e0e7ff;border:none;width:40px;height:40px;border-radius:50%;display:flex;align-items:center;justify-content:center;font-size:1.2rem;cursor:pointer;transition:all .2s}.shuffle-btn:hover{background:#c7d2fe;transform:rotate(15deg)}.shuffle-btn:active{transform:scale(.95)}.progress{font-size:1.1rem;font-weight:700;color:#334155;min-width:60px;text-align:center;font-variant-numeric:tabular-nums}@media(max-width:600px){.header{margin-bottom:30px}.header h1{font-size:2rem}.flashcard{height:400px}.controls{flex-wrap:wrap;justify-content:center}}