.b5{--paper:#f3f4ee;--paper-deep:#e3e7da;--ink:#1b2523;--ink-soft:#4b5a56;--seal:#b83a32;--seal-deep:#7e231d;--bamboo:#35544f;--bamboo-bright:#3a9a4a;--gold:#c9a85a;--rule:#cdd6c6}.b5 *{box-sizing:border-box}.b5{scroll-behavior:smooth;margin:0;background:var(--paper);background-image:radial-gradient(ellipse at 20% 10%,rgba(184,58,50,.05),transparent 40%),radial-gradient(ellipse at 80% 90%,rgba(53,84,79,.06),transparent 45%);color:var(--ink);font-family:Noto Sans,Noto Sans SC,sans-serif;line-height:1.6}.b5:before{content:"";position:fixed;inset:0;pointer-events:none;opacity:.5;background-image:url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='120' height='120'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='2' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)' opacity='0.04'/%3E%3C/svg%3E");z-index:1}.b5 .wrap{max-width:960px;margin:0 auto;padding:0 24px 120px}.b5 header.hero{padding:56px 24px 48px;text-align:center;border-bottom:1px solid var(--rule);overflow:hidden}.b5 .date-tag{font-size:.75rem;letter-spacing:.18em;color:var(--ink-soft);margin-bottom:28px}.b5 .seal-box{width:88px;height:88px;margin:0 auto 22px;border:3px solid var(--seal);border-radius:6px;display:flex;align-items:center;justify-content:center;color:var(--seal);font-family:"Noto Serif SC",serif;font-weight:900;font-size:1.5rem;transform:rotate(-3deg);box-shadow:0 0 0 1px rgba(184,58,50,.15);position:relative}.b5 .seal-box:after{content:"";position:absolute;inset:6px;border:1px solid var(--seal);border-radius:3px;opacity:.5}.b5 h1.cn{font-family:"Noto Serif SC",serif;font-weight:900;font-size:clamp(1.8rem,6vw,3rem);color:var(--ink);margin:0 0 6px;letter-spacing:.02em}.b5 .pinyin-line{font-size:1rem;color:var(--seal);font-style:italic;margin-bottom:6px}.b5 .subtitle{font-size:1rem;color:var(--ink-soft)}.b5 h1.cn .red{color:var(--seal)}.b5 .term{font-family:"Noto Serif 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var(--seal);border-radius:6px;padding:4px 10px}.b5 .back-link:hover{color:var(--seal);background:var(--paper-deep)}.b5 .lesson-nav{display:flex;justify-content:center;align-items:center;gap:14px;flex-wrap:wrap;padding:32px 24px 0}.b5 .prev-link{display:inline-block;font-size:.9rem;color:var(--ink-soft);text-decoration:none;border:1px solid var(--rule);border-radius:6px;padding:8px 16px;font-weight:700}.b5 .prev-link:hover{color:var(--seal-deep);border-color:var(--seal);background:var(--paper-deep)}.b5 .next-link{display:inline-block;font-size:.9rem;color:var(--seal-deep);text-decoration:none;border:1px solid var(--seal);border-radius:6px;padding:8px 16px;font-weight:700}.b5 .next-link:hover{color:var(--paper);background:var(--seal)}.b5 footer.pagefoot-note{text-align:center;padding:18px 24px 0;color:var(--ink-soft);font-size:.8rem;letter-spacing:.04em}.b5 .toc{border:1px solid var(--rule);background:var(--paper-deep);padding:18px 22px;margin:28px 0 26px}.b5 .toc-title{font-weight:700;color:var(--seal);font-size:.85rem;margin-bottom:12px}.b5 .toc-list{list-style:none;margin:0;padding:0;display:grid;gap:8px}.b5 .toc-list a{display:flex;align-items:baseline;gap:10px;text-decoration:none;color:var(--ink);padding:2px 0}.b5 .toc-list a:hover .toc-cn,.b5 .toc-list a:hover .toc-vn,.b5 .toc-num{color:var(--seal)}.b5 .toc-num{font-weight:700;min-width:1.8em;flex-shrink:0}.b5 .toc-cn{font-family:"Noto Serif SC",serif;font-weight:600;flex-shrink:0}.b5 .toc-vn{color:var(--ink-soft);font-size:.88rem}.b5 section{position:relative;padding:56px 0 8px;scroll-margin-top:20px}.b5 section+section{border-top:1px solid var(--rule)}.b5 .sec-head{display:flex;align-items:baseline;gap:16px;margin-bottom:30px}.b5 .sec-num{font-size:2.4rem;font-weight:900;color:var(--seal);line-height:1}.b5 .sec-num,.b5 .sec-title-cn{font-family:"Noto Serif SC",serif}.b5 .sec-title-cn{font-size:1.6rem;font-weight:600;color:var(--ink)}.b5 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