/* bilifast 介绍页的样式（中文页和英文页共用）。纯 CSS，不需要 JS；颜色跟着系统的亮色/暗色走 */
:root {
  --bg: #fcfcfb; --surface: #ffffff; --ink: #1d2129; --ink2: #4e5561; --muted: #7a808b; --line: #e6e7ea;
  --accent: #f0612e; --accent-ink: #ffffff; --accent-soft: #fff1ea;
  --direct: #5b84c9; --ext: #f0612e;
  --radius: 14px;
  color-scheme: light dark;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #15171b; --surface: #1d2025; --ink: #eceef1; --ink2: #b9bec7; --muted: #8b919b; --line: #2e3238;
    --accent: #ff7a45; --accent-ink: #1a0d06; --accent-soft: #2a1d18;
    --direct: #7ea2e0; --ext: #ff7a45;
  }
}
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0; background: var(--bg); color: var(--ink); line-height: 1.7; font-size: 17px;
  font-family: system-ui, -apple-system, "Segoe UI", "PingFang SC", "Microsoft YaHei UI", "Microsoft YaHei", "Hiragino Sans", sans-serif;
}
:lang(en) body, body:lang(en) { line-height: 1.6; }
a { color: var(--accent); text-underline-offset: 2px; }
a:hover { text-decoration-thickness: 2px; }
img, svg { max-width: 100%; height: auto; }
.wrap { max-width: 980px; margin: 0 auto; padding: 0 16px; }
@media (min-width: 720px) { .wrap { padding: 0 32px; } }

/* 顶栏 */
.top { display: flex; align-items: center; justify-content: space-between; gap: 12px; padding: 18px 0; }
.brand { display: flex; align-items: center; gap: 10px; color: var(--ink); text-decoration: none; font-weight: 700; font-size: 18px; }
.brand img { width: 40px; height: 40px; margin: -5px; }
.top nav { display: flex; gap: 18px; font-size: 15px; }
.top nav a { color: var(--ink2); text-decoration: none; }
.top nav a:hover { color: var(--ink); }

/* 首屏 */
.hero { display: grid; gap: 32px; align-items: center; padding: 24px 0 56px; }
@media (min-width: 820px) { .hero { grid-template-columns: 1fr 300px; gap: 48px; padding: 40px 0 72px; } }
.hero h1 { margin: 0; font-size: clamp(30px, 5.4vw, 46px); line-height: 1.25; letter-spacing: -.01em; text-wrap: balance; }
.hero h1 em { font-style: normal; color: var(--accent); }
.lead { margin: 18px 0 0; font-size: 19px; color: var(--ink2); max-width: 36em; }
.cta { display: flex; flex-wrap: wrap; gap: 12px; margin-top: 28px; }
.btn { display: inline-flex; align-items: center; gap: 8px; padding: 12px 20px; border-radius: 999px; font-weight: 600;
       font-size: 16px; text-decoration: none; border: 1px solid var(--line); color: var(--ink); background: var(--surface); }
.btn.primary { background: var(--accent); border-color: var(--accent); color: var(--accent-ink); }
.btn:hover { text-decoration: none; filter: brightness(1.05); }
.btn svg { width: 18px; height: 18px; flex: none; }
.facts { display: flex; flex-wrap: wrap; gap: 8px 20px; margin: 22px 0 0; padding: 0; list-style: none; font-size: 15px; color: var(--muted); }
.facts li::before { content: "✓"; color: var(--accent); margin-right: 6px; font-weight: 700; }
.shot { margin: 0; justify-self: center; }
.shot img { display: block; width: 300px; border-radius: var(--radius); border: 1px solid var(--line);
            box-shadow: 0 12px 40px rgba(20, 22, 28, .12); }
.shot figcaption { margin-top: 10px; font-size: 13px; color: var(--muted); text-align: center; max-width: 300px; }

/* 各节 */
section { padding: 56px 0; border-top: 1px solid var(--line); }
section h2 { margin: 0 0 8px; font-size: clamp(24px, 3.6vw, 30px); line-height: 1.3; }
.sub { margin: 0 0 28px; color: var(--ink2); max-width: 44em; }

/* 实测对比 */
.legend { display: flex; flex-wrap: wrap; gap: 8px 24px; margin: 0 0 12px; font-size: 15px; color: var(--ink2); }
.legend span { display: inline-flex; align-items: center; gap: 8px; }
.legend i { width: 22px; height: 10px; border-radius: 0 3px 3px 0; }
.chart { margin: 0; }
.row { display: grid; gap: 6px; padding: 16px 0; border-top: 1px solid var(--line); }
.row:last-child { border-bottom: 1px solid var(--line); }
@media (min-width: 720px) { .row { grid-template-columns: 200px 1fr; gap: 20px; align-items: center; } }
.phase { font-weight: 600; }
.phase small { display: block; font-weight: 400; font-size: 14px; color: var(--muted); }
.bars { display: grid; gap: 6px; }
.bar { display: grid; grid-template-columns: minmax(0, 1fr); gap: 2px; }
@media (min-width: 720px) { .bar { grid-template-columns: minmax(0, 1fr) 260px; gap: 12px; align-items: center; } }
.track { height: 14px; }
.track b { display: block; height: 100%; min-width: 3px; border-radius: 0 4px 4px 0; }
.bar.d b { background: var(--direct); }
.bar.e b { background: var(--ext); }
.bar span { font-size: 15px; color: var(--ink2); }
.bar.e span { color: var(--ink); font-weight: 600; }
.note { margin: 16px 0 0; font-size: 14px; color: var(--muted); }

/* 原理 */
.how { display: grid; gap: 24px; }
@media (min-width: 820px) { .how { grid-template-columns: 1fr 1fr; } }
.panel { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); padding: 20px; }
.panel h3 { margin: 0 0 4px; font-size: 18px; }
.panel p { margin: 0 0 14px; font-size: 15px; color: var(--ink2); }
.diagram { display: block; width: 100%; }
.diagram text { font: 13px system-ui, -apple-system, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif; fill: var(--ink2); }
.diagram .box { fill: var(--bg); stroke: var(--line); }
.diagram .slow { stroke: var(--direct); }
.diagram .fast { stroke: var(--ext); }
.diagram .label { fill: var(--ink); font-weight: 600; }

/* 用法 */
.steps { display: grid; gap: 16px; margin: 0; padding: 0; list-style: none; counter-reset: s; }
@media (min-width: 720px) { .steps { grid-template-columns: repeat(3, 1fr); } }
.steps li { counter-increment: s; background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); padding: 20px; }
.steps li::before { content: counter(s); display: grid; place-items: center; width: 30px; height: 30px; border-radius: 50%;
                    background: var(--accent-soft); color: var(--accent); font-weight: 700; margin-bottom: 10px; }
.steps h3 { margin: 0 0 4px; font-size: 17px; }
.steps p { margin: 0; font-size: 15px; color: var(--ink2); }

/* 隐私、常见问题 */
.plain { max-width: 46em; }
.plain ul { padding-left: 1.2em; }
.plain li { margin: 4px 0; }
.faq h3 { margin: 28px 0 6px; font-size: 18px; }
.faq h3:first-of-type { margin-top: 8px; }
.faq p { margin: 0; color: var(--ink2); max-width: 46em; }

/* 页脚 */
footer { padding: 32px 0 48px; border-top: 1px solid var(--line); font-size: 14px; color: var(--muted); }
footer p { margin: 4px 0; }
footer a { color: var(--ink2); }