:root{--bg: #f7f8fa;--card: #ffffff;--primary: #ff6b35;--primary-dark: #e8551f;--text: #1f2430;--muted: #8a93a3;--ring: #ffd9c7;font-family:-apple-system,BlinkMacSystemFont,PingFang SC,Segoe UI,sans-serif}*{box-sizing:border-box}body{margin:0;background:var(--bg);color:var(--text);-webkit-tap-highlight-color:transparent}.app{max-width:480px;margin:0 auto;min-height:100vh;display:flex;flex-direction:column;background:var(--bg)}.screen{flex:1;display:flex;flex-direction:column;padding:16px}.card{background:var(--card);border-radius:16px;padding:20px;box-shadow:0 2px 12px #0000000d}.btn-primary{-webkit-appearance:none;-moz-appearance:none;appearance:none;border:none;width:100%;padding:18px;border-radius:16px;background:var(--primary);color:#fff;font-size:20px;font-weight:700;cursor:pointer}.btn-primary:active{background:var(--primary-dark)}.btn-primary:disabled{opacity:.5}.btn-ghost{-webkit-appearance:none;-moz-appearance:none;appearance:none;background:transparent;border:1px solid var(--ring);color:var(--primary-dark);border-radius:12px;padding:10px 14px;font-size:15px;cursor:pointer}.muted{color:var(--muted)}.center{display:flex;align-items:center;justify-content:center}@keyframes caret-blink{0%,to{opacity:1}50%{opacity:0}}.caret{animation:caret-blink 1s step-end infinite}.bubble-row{position:relative;display:flex;margin:8px 0}.bubble-row.ai{justify-content:flex-start}.bubble-row.student{justify-content:flex-end}.bubble{position:relative;max-width:78%;padding:10px 14px;border-radius:16px;box-shadow:0 1px 4px #0000000f}.bubble.ai{background:#fff;color:var(--text)}.bubble.student{background:var(--primary);color:#fff}.replay-btn{position:absolute;right:4px;bottom:-12px;width:22px;height:22px;padding:0;border:none;border-radius:50%;background:#fff;color:var(--primary-dark);font-size:10px;line-height:22px;text-align:center;cursor:pointer;box-shadow:0 1px 4px #0000002e;opacity:0;transition:opacity .15s ease}.bubble-row:hover .replay-btn,.replay-btn:focus-visible{opacity:1}