*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
body{font-family:"Noto Sans SC",system-ui,sans-serif;background:#fff;color:#1a1a1a;line-height:1.75;font-size:16px}
a{color:#0d9488;text-decoration:none}
a:hover{text-decoration:underline}
img{max-width:100%;height:auto;display:block}
.container{max-width:1140px;margin:0 auto;padding:0 20px}

.site-header{background:#fff;border-bottom:1px solid #e8e8e8;position:sticky;top:0;z-index:100}
.header-row{display:flex;align-items:center;justify-content:space-between;padding:14px 0}
.brand{display:flex;align-items:center;gap:10px;font-size:1.05rem;color:#1a1a1a;font-weight:500}
.brand:hover{text-decoration:none}
.brand b{color:#0d9488;font-weight:700}
.site-nav ul{display:flex;gap:6px 18px;list-style:none;flex-wrap:wrap}
.site-nav a{color:#444;font-size:.92rem;padding:4px 0}
.site-nav a.active{color:#0d9488;font-weight:600;border-bottom:2px solid #0d9488}
.nav-toggle{display:none;background:none;border:none;cursor:pointer;padding:8px;flex-direction:column;gap:5px}
.nav-toggle span{display:block;width:22px;height:2px;background:#333;transition:.2s}
.nav-toggle.is-open span:nth-child(1){transform:translateY(7px) rotate(45deg)}
.nav-toggle.is-open span:nth-child(2){opacity:0}
.nav-toggle.is-open span:nth-child(3){transform:translateY(-7px) rotate(-45deg)}

.ads-top-bar{background:#fafafa;border-bottom:1px solid #eee;padding:10px 0}
.applist-title{font-size:.78rem;color:#888;text-align:center;margin-bottom:6px;letter-spacing:.05em}
#ads{display:flex;justify-content:center;flex-wrap:wrap;gap:12px}
#ads .caption{font-size:.7rem;color:#666;margin-top:4px;text-align:center;max-width:70px;line-height:1.3}

/* Rail chapter layout */
.hero-rail{padding:40px 0 32px;border-bottom:1px solid #eee}
.hero-rail h1{font-size:1.72rem;line-height:1.35;margin-bottom:18px;color:#111;max-width:820px}
.hero-rail .lead{color:#444;margin-bottom:14px;font-size:1.02rem;max-width:820px}
.hero-rail .lead:last-of-type{margin-bottom:0}

.rail-shell{display:grid;grid-template-columns:220px 1fr;gap:36px;padding:36px 0 20px;align-items:start}
.rail-nav{position:sticky;top:88px}
.rail-nav-title{font-size:.75rem;font-weight:600;letter-spacing:.1em;text-transform:uppercase;color:#888;margin-bottom:16px}
.rail-nav ol{list-style:none;counter-reset:rail}
.rail-nav li{counter-increment:rail;position:relative;padding-left:36px;margin-bottom:4px}
.rail-nav li::before{content:counter(rail);position:absolute;left:0;top:50%;transform:translateY(-50%);width:24px;height:24px;border-radius:50%;background:#f0fdfa;border:2px solid #99f6e4;color:#0d9488;font-size:.75rem;font-weight:700;display:flex;align-items:center;justify-content:center;line-height:1}
.rail-nav li:not(:last-child)::after{content:"";position:absolute;left:11px;top:calc(50% + 14px);width:2px;height:calc(100% + 4px);background:#ccfbf1}
.rail-nav a{display:block;padding:10px 0;font-size:.88rem;color:#555;line-height:1.35}
.rail-nav a:hover,.rail-nav a.is-active{color:#0d9488;font-weight:600;text-decoration:none}

.rail-panels{display:flex;flex-direction:column;gap:28px}
.rail-chapter{background:#fff;border:1px solid #e8e8e8;border-radius:10px;padding:28px 32px;scroll-margin-top:96px;transition:border-color .2s,box-shadow .2s}
.rail-chapter:hover{border-color:#99f6e4;box-shadow:0 4px 18px rgba(13,148,136,.05)}
.rail-chapter .chap-num{display:inline-block;font-size:.72rem;font-weight:600;letter-spacing:.06em;color:#0d9488;background:#f0fdfa;padding:3px 10px;border-radius:4px;margin-bottom:12px}
.rail-chapter h2{font-size:1.18rem;margin-bottom:14px;color:#111;line-height:1.4}
.rail-chapter p{margin-bottom:10px;color:#333;font-size:.97rem}
.rail-chapter p:last-child{margin-bottom:0}
.rail-chapter figure{margin:16px 0 0}
.rail-chapter figcaption{font-size:.82rem;color:#777;margin-top:6px}
.rail-chapter ul{margin:10px 0 10px 20px;color:#333;font-size:.95rem}
.rail-chapter li{margin-bottom:6px}

.callout-teal{background:#f0fdfa;border-left:3px solid #0d9488;padding:14px 18px;margin:16px 0;border-radius:0 8px 8px 0;font-size:.93rem;color:#134e4a}
.callout-warn{background:#fffbeb;border-left:3px solid #d97706;padding:14px 18px;margin:16px 0;border-radius:0 8px 8px 0;font-size:.93rem;color:#78350f}

.split-duo{display:grid;grid-template-columns:1fr 1fr;gap:20px;margin:16px 0}
.split-duo .duo-box{background:#fafafa;border:1px solid #eee;border-radius:8px;padding:16px 18px}
.split-duo h3{font-size:.95rem;margin-bottom:8px;color:#222}

.faq{padding:36px 0 48px;border-top:1px solid #eee}
.faq h2{font-size:1.25rem;margin-bottom:18px;color:#111}
.faq details{border:1px solid #e8e8e8;border-radius:8px;margin-bottom:10px;padding:0}
.faq summary{padding:14px 18px;cursor:pointer;font-weight:500;color:#222;list-style:none}
.faq summary::-webkit-details-marker{display:none}
.faq details[open] summary{border-bottom:1px solid #eee;background:#fafafa}
.faq details p{padding:14px 18px;color:#444;font-size:.95rem}

.site-footer{background:#fafafa;border-top:1px solid #eee;padding:28px 0;margin-top:20px;text-align:center;font-size:.88rem;color:#666}
.footer-links{display:flex;flex-wrap:wrap;justify-content:center;gap:8px 16px;margin-bottom:10px}
.footer-links a{color:#555}

.prose-page{padding:32px 0 48px}
.prose-page h1{font-size:1.5rem;margin-bottom:16px}
.prose-page h2{font-size:1.15rem;margin:24px 0 10px;color:#222}
.prose-page p{margin-bottom:12px;color:#333}
.error-page{text-align:center;padding:48px 0 24px}
.error-page h1{font-size:3rem;color:#0d9488}

@media(max-width:860px){
  .rail-shell{grid-template-columns:1fr;gap:20px}
  .rail-nav{position:static;border-bottom:1px solid #eee;padding-bottom:16px}
  .rail-nav ol{display:flex;flex-wrap:wrap;gap:8px}
  .rail-nav li{padding-left:0;margin-bottom:0}
  .rail-nav li::before{position:static;transform:none;display:inline-flex;margin-right:6px;vertical-align:middle}
  .rail-nav li::after{display:none}
  .rail-nav a{display:inline;padding:6px 12px;border:1px solid #e8e8e8;border-radius:20px;font-size:.82rem;background:#fafafa}
  .split-duo{grid-template-columns:1fr}
  .nav-toggle{display:flex}
  .site-nav{position:absolute;top:100%;left:0;right:0;background:#fff;border-bottom:1px solid #eee;padding:12px 20px;display:none}
  .site-nav.is-open{display:block}
  .site-nav ul{flex-direction:column;gap:10px}
  .header-row{position:relative}
}