:root {
      color-scheme: light dark;
      --bg: #ffffff; --bg-alt: #f5f6f8; --fg: #16181d; --muted: #5b616e; --border: #e2e5ea;
      --accent: #2f5bea; --accent-fg: #ffffff; --radius: 14px; --max: 60rem;
      font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", "PingFang SC", "Hiragino Sans GB", Arial, sans-serif;
    }
    @media (prefers-color-scheme: dark) {
      :root { --bg: #0f1115; --bg-alt: #171a20; --fg: #e9ebef; --muted: #a0a6b2; --border: #262a32; --accent: #7c9cff; --accent-fg: #0f1115; }
    }
    *, *::before, *::after { box-sizing: border-box; }
    body { margin: 0; background: var(--bg); color: var(--fg); line-height: 1.6; }
    .wrap { max-width: var(--max); margin: 0 auto; padding: 0 1.25rem; }
    header { border-bottom: 1px solid var(--border); }
    header .wrap { display: flex; align-items: center; justify-content: space-between; height: 3.5rem; }
    .brand { font-weight: 700; font-size: 1.15rem; color: var(--fg); text-decoration: none; letter-spacing: -0.01em; }
    .brand span { color: var(--accent); }
    .brand small { font-weight: 500; color: var(--muted); margin-left: .4rem; }
    .lang { font-size: .9rem; color: var(--muted); }
    .lang a { color: inherit; }
    .hero { padding: 3rem 0 3rem; }
    h1 { font-size: clamp(2rem, 5vw, 3.1rem); line-height: 1.15; margin: 0 0 1rem; letter-spacing: -0.02em; }
    .lead { font-size: 1.2rem; color: var(--muted); max-width: 40rem; margin: 0 0 2rem; }
    .cta { display: inline-block; background: var(--accent); color: var(--accent-fg); padding: .8rem 1.4rem; border-radius: 999px;
           font-weight: 600; text-decoration: none; }
    .note { color: var(--muted); font-size: .95rem; margin-top: .9rem; }
    section { padding: 3rem 0; border-top: 1px solid var(--border); }
    h2 { font-size: 1.5rem; margin: 0 0 1.5rem; letter-spacing: -0.01em; }
    .grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(15rem, 1fr)); gap: 1rem; }
    .card { background: var(--bg-alt); border: 1px solid var(--border); border-radius: var(--radius); padding: 1.25rem 1.3rem; }
    .card h3 { margin: 0 0 .4rem; font-size: 1.05rem; }
    .card p { margin: 0; color: var(--muted); }
    ol.steps { margin: 0; padding-left: 1.2rem; }
    ol.steps li { margin: .5rem 0; }
    ol.steps b { color: var(--fg); }
    .zh { display: none; }
    html[lang="zh"] .zh { display: revert; }
    html[lang="zh"] .en { display: none; }
    .demo video { width: 100%; aspect-ratio: 4 / 3; background: #000; border-radius: var(--radius); display: block; }
    .demo .bar { display: flex; flex-wrap: wrap; gap: .5rem; align-items: center; margin: 1rem 0 .4rem; }
    .demo .bar button { font: inherit; font-size: .95rem; padding: .45rem .95rem; border-radius: 999px; cursor: pointer;
                        border: 1px solid var(--border); background: var(--bg-alt); color: var(--fg); }
    .demo .bar button[aria-pressed="true"] { background: var(--accent); border-color: var(--accent); color: var(--accent-fg); }
    .demo .bar .subs { margin-left: auto; font-size: .9rem; color: var(--muted); display: flex; gap: .35rem; align-items: center; }
    .demo .bar .subs select { font: inherit; font-size: .9rem; padding: .25rem .4rem; border-radius: 8px;
                              border: 1px solid var(--border); background: var(--bg); color: var(--fg); }
    .demo .cap { color: var(--muted); font-size: .9rem; margin: .4rem 0 0; }
    footer { border-top: 1px solid var(--border); padding: 2rem 0 3rem; color: var(--muted); font-size: .9rem; }
    nav.top { display: flex; gap: 1.1rem; align-items: center; font-size: .95rem; }
    nav.top a { color: var(--muted); text-decoration: none; }
    nav.top a[aria-current="page"], nav.top a:hover { color: var(--fg); }
    .hero .player { margin-top: 1.5rem; max-width: 46rem; }
    form.contact { display: grid; gap: 1rem; max-width: 36rem; }
    form.contact label { display: grid; gap: .35rem; font-weight: 600; font-size: .95rem; }
    form.contact input, form.contact textarea, form.contact select { font: inherit; font-weight: 400; padding: .65rem .8rem;
        border-radius: 10px; border: 1px solid var(--border); background: var(--bg-alt); color: var(--fg); }
    form.contact textarea { min-height: 9rem; resize: vertical; }
    form.contact button { justify-self: start; font: inherit; font-weight: 600; border: 0; cursor: pointer; }
    .hp { position: absolute; left: -10000px; width: 1px; height: 1px; overflow: hidden; }
    .msg { padding: 1rem 1.2rem; border-radius: var(--radius); border: 1px solid var(--border); background: var(--bg-alt); }