:root{--bg: #fafaf8;--fg: #1c1c1a;--muted: #6b6b66;--line: #e4e3de;--card: #fff;--accent: #1f5f4a;--right: #1f7a4d;--wrong: #b3372b;font-family:system-ui,-apple-system,Segoe UI,sans-serif;color:var(--fg);background:var(--bg)}@media (prefers-color-scheme: dark){:root{--bg: #151514;--fg: #ecebe6;--muted: #9a9993;--line: #2c2c2a;--card: #1d1d1b;--accent: #6cc3a0;--right: #5fcf93;--wrong: #f07b6e}}*{box-sizing:border-box}body{margin:0}.shell{max-width:820px;margin:0 auto;padding:0 16px 64px}.nav{display:flex;justify-content:space-between;align-items:center;padding:20px 0;border-bottom:1px solid var(--line);margin-bottom:32px}.nav a{color:var(--muted);text-decoration:none;margin-left:20px}.nav a.active,.nav .brand{color:var(--fg)}.brand{font-weight:700;margin-left:0!important}.hero h1{font-size:clamp(28px,5vw,40px);line-height:1.15;margin:24px 0 12px}.hero p{color:var(--muted);font-size:18px;line-height:1.5;max-width:60ch}.button{display:inline-block;background:var(--accent);color:var(--bg);border:0;border-radius:8px;padding:10px 18px;font:inherit;font-weight:600;cursor:pointer;text-decoration:none;margin-top:12px}.button:disabled{opacity:.45;cursor:default}.tabs{display:flex;gap:6px;flex-wrap:wrap;margin-bottom:20px}.tabs button{background:none;border:1px solid var(--line);color:var(--fg);border-radius:999px;padding:6px 14px;font:inherit;cursor:pointer}.tabs button.active{background:var(--fg);color:var(--bg)}.card{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:20px}.meta,.muted{color:var(--muted);font-size:14px}.stem{font-size:17px;line-height:1.55}.choices{list-style:none;padding:0}.choice{width:100%;text-align:left;background:none;border:1px solid var(--line);color:var(--fg);border-radius:8px;padding:10px 12px;margin:6px 0 0;font:inherit;cursor:pointer}.choice.picked{border-color:var(--accent)}.choice.right{border-color:var(--right)}.choice.wrong{border-color:var(--wrong)}.rationale{color:var(--muted);font-size:14px;margin:4px 0 8px 12px}.right-text{color:var(--right);font-weight:600}.wrong-text,.error{color:var(--wrong);font-weight:600}.mastery{width:100%;border-collapse:collapse}.mastery th,.mastery td{text-align:left;padding:8px;border-bottom:1px solid var(--line);font-size:14px}.bar{display:inline-block;width:90px;height:6px;background:var(--line);border-radius:3px;margin-right:8px;vertical-align:middle}.bar span{display:block;height:100%;background:var(--accent);border-radius:3px}