:root{--ink:#1d2430;--mute:#5b6675;--line:#e3e7ec;--acc:#1f6feb;--ok:#2e8b57;--bad:#c0392b;--bg:#fafbfc;--card:#fff}
*{box-sizing:border-box}body{margin:0;font-family:-apple-system,Segoe UI,Helvetica,Arial,sans-serif;color:var(--ink);background:var(--bg);line-height:1.5}
header{background:#fff;border-bottom:1px solid var(--line)}header .in{max-width:860px;margin:0 auto;padding:12px 20px;display:flex;gap:16px;align-items:center;flex-wrap:wrap}
header a{color:var(--mute);text-decoration:none;font-size:14px}header a.brand{color:var(--ink);font-weight:700;font-size:16px}header a.home{color:#fff;background:var(--acc);padding:4px 10px;border-radius:999px;font-weight:600}
main{max-width:860px;margin:0 auto;padding:24px 20px 80px}h1{font-size:28px;margin:8px 0 4px}h2{font-size:20px;margin:28px 0 8px}h3{font-size:16px;margin:20px 0 6px}
.sub{color:var(--mute);margin:0 0 18px}.card{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:18px 20px;margin:14px 0}
.take{background:#eef4ff;border-color:#c9daff}.take h2{margin-top:0}
.tabs{display:flex;gap:8px;margin:12px 0}.tabs button{border:1px solid var(--line);background:#fff;padding:8px 14px;border-radius:999px;cursor:pointer;font-size:14px}.tabs button.on{background:var(--acc);color:#fff;border-color:var(--acc)}
.pane{display:none}.pane.on{display:block}video{width:100%;border-radius:10px;background:#000;max-height:480px}
.placeholder{border:2px dashed #c9d2dd;border-radius:10px;padding:18px;color:var(--mute);background:#fff}
.story{width:100%;border-collapse:collapse;font-size:14px}.story td,.story th{border-top:1px solid var(--line);padding:6px 8px;vertical-align:top;text-align:left}.story td:last-child{color:var(--mute);width:42%}
article p{margin:10px 0;font-size:17px}article h3{color:var(--acc)}article table{border-collapse:collapse;margin:12px 0;font-size:15px;width:100%}article td,article th{border:1px solid var(--line);padding:6px 10px;text-align:left}
.rule{background:#fff8e1;border-left:4px solid #f0b429;padding:10px 14px;border-radius:6px;margin:16px 0;font-size:17px}.rule p{margin:4px 0}
svg.fig{width:100%;max-width:520px;display:block;margin:10px auto;border:1px solid var(--line);border-radius:8px}
.q{border:1px solid var(--line);border-radius:10px;padding:14px 16px;margin:12px 0;background:#fff}.q .stem{font-size:16px;margin:0 0 10px}.q .n{color:var(--mute);font-size:12px;letter-spacing:.04em;text-transform:uppercase}
.opts{display:flex;flex-direction:column;gap:8px}.opts button{text-align:left;border:1px solid var(--line);background:#fff;border-radius:8px;padding:10px 12px;font-size:15px;cursor:pointer}
.opts button.right{border-color:var(--ok);background:#e9f7ef}.opts button.wrong{border-color:var(--bad);background:#fdecea}.opts button:disabled{cursor:default}
.why{display:none;margin-top:10px;padding:10px 12px;border-radius:8px;background:#f3f5f8;font-size:15px}.why.on{display:block}.why b.ok{color:var(--ok)}.why b.bad{color:var(--bad)}
input.txt{font-size:16px;padding:8px 10px;border:1px solid var(--line);border-radius:8px;width:60%}textarea{width:100%;min-height:70px;font-size:15px;padding:8px;border:1px solid var(--line);border-radius:8px}
button.go{border:0;background:var(--acc);color:#fff;padding:9px 14px;border-radius:8px;font-size:15px;cursor:pointer;margin-left:6px}
.nav{display:flex;justify-content:space-between;margin-top:30px}.nav a{text-decoration:none;color:#fff;background:var(--acc);padding:10px 16px;border-radius:8px}.nav a.prev{background:#fff;color:var(--acc);border:1px solid var(--acc)}
.steps{list-style:none;padding:0;margin:0}.steps li{display:flex;gap:12px;align-items:center;padding:10px 0;border-top:1px solid var(--line)}.steps li:first-child{border-top:0}.steps .k{min-width:84px;color:var(--mute);font-size:13px;text-transform:uppercase;letter-spacing:.04em}.steps a{color:var(--ink);text-decoration:none;font-weight:600}.steps .m{margin-left:auto;color:var(--mute);font-size:13px}
details{margin:10px 0}summary{cursor:pointer;color:var(--acc)}
.poll button{margin:4px 6px 4px 0}
blockquote{border-left:3px solid #c9d2dd;margin:8px 0;padding:4px 12px;color:var(--mute)}
.pill{display:inline-block;font-size:12px;padding:2px 8px;border-radius:999px;background:#eef1f5;color:var(--mute);margin-right:6px}
code{background:#f3f5f8;padding:1px 4px;border-radius:4px;font-size:90%}