*{box-sizing:border-box}body{color:#172033;background:#f5f7fb;min-width:320px;min-height:100vh;margin:0;font-family:Inter,ui-sans-serif,system-ui,-apple-system,BlinkMacSystemFont,Segoe UI,sans-serif}button{font:inherit}.practice-page{width:min(100%,520px);min-height:100vh;margin:0 auto;padding:18px 16px 28px}.topbar{justify-content:space-between;align-items:center;margin-bottom:22px;display:flex}.brand{color:#073b70;letter-spacing:.04em;font-size:20px;font-weight:800}.subtitle{color:#68758a;margin-top:2px;font-size:14px}.qa-badge{color:#075985;background:#e7f5ff;border-radius:999px;place-items:center;min-width:42px;height:32px;padding:0 10px;font-size:12px;font-weight:800;display:grid}.question-card{background:#fff;border:1px solid #e4e9f1;border-radius:22px;padding:22px 18px 20px;box-shadow:0 12px 30px #0f172a0f}.question-meta{color:#68758a;justify-content:space-between;gap:10px;margin-bottom:18px;font-size:13px;font-weight:600;display:flex}h1{color:#172033;margin:0 0 20px;font-size:clamp(20px,5vw,26px);line-height:1.25}.expression{background:#f7faff;border-radius:18px;place-items:center;min-height:110px;margin-bottom:20px;padding:18px;font-size:clamp(22px,7vw,34px);display:grid;overflow:hidden}.expression .katex-display{margin:0}.options{gap:12px;display:grid}.option-button{color:#172033;text-align:left;cursor:pointer;background:#fff;border:2px solid #e1e7ef;border-radius:16px;align-items:center;gap:14px;width:100%;min-height:62px;padding:10px 16px;transition:border-color .12s,background .12s,transform .12s;display:flex}.option-button:not(:disabled):active{transform:scale(.99)}.option-button.selected{background:#f0f7ff;border-color:#1d72d8}.option-button.correct{background:#effbf5;border-color:#169b62}.option-button.incorrect{background:#fff3f3;border-color:#d94444}.option-letter{background:#edf2f7;border-radius:50%;flex:0 0 38px;place-items:center;width:38px;height:38px;font-weight:800;display:grid}.option-button.selected .option-letter{color:#075eae;background:#dbeeff}.option-button.correct .option-letter{color:#087547;background:#d8f4e6}.option-button.incorrect .option-letter{color:#b42323;background:#ffe1e1}.option-math{flex:1;place-items:center;font-size:22px;display:grid}.primary-button{color:#fff;cursor:pointer;background:#075eae;border:0;border-radius:15px;width:100%;min-height:54px;margin-top:18px;padding:12px 18px;font-weight:800}.primary-button:disabled{opacity:.42;cursor:not-allowed}.feedback{border-radius:16px;margin-top:18px;padding:16px;line-height:1.5}.correct-feedback{color:#075b39;background:#effbf5}.incorrect-feedback{color:#8a4312;background:#fff7ed}.explanation{margin-top:14px;font-size:18px;overflow-x:auto}.explanation .katex-display{margin:.6em 0}.qa-footer{color:#8994a6;flex-wrap:wrap;justify-content:space-between;gap:8px;margin-top:14px;padding:0 4px;font-family:ui-monospace,SFMono-Regular,Menlo,monospace;font-size:10px;display:flex}@media (width>=430px){.practice-page{padding-left:20px;padding-right:20px}.question-card{padding:26px 24px}}