:root{--paper:#f5f8fb;--surface:#fff;--ink:#183248;--muted:#536a7a;--line:#d6e1e9;--blue:#245aa5;--tint:#eaf1fa}*{box-sizing:border-box}html{scroll-behavior:smooth}body{background:var(--paper);color:var(--ink);margin:0;font-family:PingFang SC,Microsoft YaHei,sans-serif;line-height:1.7}a{color:inherit;text-decoration:none}a:focus-visible{outline:3px solid var(--blue);outline-offset:6px}.skip-link{z-index:2;background:#fff;padding:8px 16px;position:absolute;top:-80px;left:20px}.skip-link:focus{top:12px}.masthead,main,footer{width:min(1080px,100% - 80px);margin-inline:auto}.masthead{border-bottom:1px solid var(--line);justify-content:space-between;align-items:center;padding-block:28px;display:flex}.brand{letter-spacing:.06em;align-items:center;gap:12px;font-weight:600;display:inline-flex}.brand-mark{background:var(--blue);color:#fff;border-radius:4px 10px 4px 4px;place-items:center;width:32px;height:35px;font-family:Songti SC,serif;display:grid}.status,.label{color:var(--muted);letter-spacing:.08em;font-size:12px}.status:before{content:"";background:var(--muted);vertical-align:middle;border-radius:50%;width:6px;height:6px;margin-right:8px;display:inline-block}.intro{padding:76px 0 60px}.eyebrow{letter-spacing:.12em;color:var(--blue);font-size:12px}h1{letter-spacing:.02em;margin:20px 0 24px;font-family:Songti SC,STSong,Noto Serif CJK SC,serif;font-size:clamp(38px,5vw,62px);font-weight:600;line-height:1.35}.lead{color:var(--muted);font-size:16px;line-height:1.95}.text-link{color:var(--blue);border-bottom:1px solid var(--blue);align-items:center;gap:28px;margin-top:18px;padding-bottom:4px;font-size:14px;display:inline-flex}.lesson{background:var(--surface);border:1px solid var(--line);border-left:4px solid var(--blue);border-radius:0 12px 12px 0;padding:30px 34px 22px;scroll-margin-top:28px}.lesson-heading{justify-content:space-between;align-items:center;gap:16px;display:flex}.label{background:var(--tint);white-space:nowrap;border-radius:4px;padding:3px 10px}.lesson-body{grid-template-columns:1.5fr 1fr;gap:60px;margin:28px 0;display:grid}h2{margin:0;font-size:27px;font-weight:600}.lesson-question{margin:8px 0 18px;font-size:18px}.muted{color:var(--muted);font-size:14px}.lesson-meta{border-left:1px solid var(--line);gap:14px;margin:0;padding-left:30px;display:grid}dt{color:var(--muted);font-size:12px}dd{margin:3px 0 0;font-size:14px}.notice{border-top:1px solid var(--line);color:var(--muted);margin:0;padding-top:18px;font-size:12px}.approach{grid-template-columns:repeat(3,1fr);gap:42px;margin:48px 0 62px;display:grid}.approach span{color:var(--blue);font:12px ui-monospace,monospace}h3{margin:9px 0;font-size:16px;font-weight:600}.approach p{color:var(--muted);margin:0;font-size:13px}footer{border-top:1px solid var(--line);color:var(--muted);justify-content:space-between;padding:24px 0 32px;font-size:12px;display:flex}@media (max-width:640px){.masthead,main,footer{width:calc(100% - 40px)}.masthead{padding-block:22px}.intro{padding:48px 0 40px}.desktop-break{display:none}.lead{font-size:15px}.lesson{padding:24px 20px 20px}.lesson-heading{align-items:flex-start}.lesson-body{grid-template-columns:1fr;gap:24px;margin:24px 0}.lesson-meta{border-left:0;border-top:1px solid var(--line);padding:20px 0 0}.approach{grid-template-columns:1fr;gap:26px;margin:32px 0 40px}.approach>div{grid-template-columns:30px 1fr;column-gap:12px;display:grid}.approach span{padding-top:7px}h3{margin:0}.approach p{grid-column:2;margin-top:5px}footer{gap:20px}}@media (prefers-reduced-motion:reduce){html{scroll-behavior:auto}}.account-page{max-width:800px;padding-block:36px 70px}.account-page>.eyebrow{margin-top:48px}.account-page h1{font-size:clamp(34px,5vw,48px)}.account-page .lesson{margin-top:32px}.account-page form{border-top:1px solid var(--line);margin-top:28px;padding-top:16px}.account-page button,.button-link{background:var(--blue);color:#fff;font:inherit;cursor:pointer;border:0;border-radius:6px;margin-top:18px;padding:12px 20px;display:inline-block}button:focus-visible,input:focus-visible{outline:3px solid var(--blue);outline-offset:5px}.confirm{font-size:14px;display:block}.account-id{overflow-wrap:anywhere;font-family:ui-monospace,monospace}.steps{padding-left:24px}.steps li{padding:10px 0}.steps p{color:var(--muted)}.masthead nav{align-items:center;gap:24px;font-size:13px;display:flex}@media (max-width:640px){.masthead nav{gap:12px;font-size:12px}.masthead nav .status{display:none}}.course-reader{max-width:860px}.course-reader h1{font-size:clamp(2rem,5vw,3.5rem)}.course-reader section{margin:3rem 0;scroll-margin-top:2rem}.course-reader p,.course-reader li{line-height:1.9}.course-reader nav{border:1px solid var(--line,#d9d9d2);padding:1rem 1.5rem}.course-reader table{border-collapse:collapse;max-width:100%;display:block;overflow-x:auto}.course-reader td,.course-reader th{text-align:left;border:1px solid #d9d9d2;padding:.6rem}.course-reader pre{white-space:pre-wrap;overflow-wrap:anywhere;background:#eeeae2;padding:1rem}.course-reader blockquote{border-left:3px solid #7b826a;margin-left:0;padding-left:1rem}