:root{color-scheme:light dark;--bg:#f2f0e9;--panel:#faf9f4;--ink:#242720;--muted:#62665b;--line:#d3d5c7;--accent:#526b35;--tint:#e7ecd9;--code:#20271e;--code-ink:#eceddb;--serif:"Songti SC","Noto Serif CJK SC",Georgia,serif;--sans:"Avenir Next","PingFang SC","Microsoft YaHei",sans-serif}
@media(prefers-color-scheme:dark){:root{--bg:#171c18;--panel:#1e251f;--ink:#eeeede;--muted:#a9b0a2;--line:#3c493c;--accent:#bfd78e;--tint:#2c3827;--code:#101610;--code-ink:#e4edd5}}
*{box-sizing:border-box}html{scroll-behavior:smooth;scroll-padding-top:20px}body{margin:0;background:var(--bg);color:var(--ink);font:16px/1.8 var(--sans);overflow-wrap:anywhere}button,input{font:inherit}a{color:var(--accent);text-underline-offset:4px}button,.file-button{border:1px solid var(--line);background:transparent;color:var(--ink);padding:9px 15px;cursor:pointer;border-radius:3px;display:inline-flex;align-items:center;justify-content:center;min-height:44px;text-align:center}button:hover,.file-button:hover{background:var(--tint)}button.primary{background:var(--accent);border-color:var(--accent);color:var(--bg)}:focus-visible{outline:3px solid var(--accent);outline-offset:4px}.topbar{max-width:1440px;margin:auto;padding:27px 5vw;border-bottom:1px solid var(--line);display:flex;justify-content:space-between;align-items:center;gap:20px}.brand-row{display:flex;align-items:center;gap:18px;min-width:0}.brand{text-decoration:none;color:var(--ink);font:24px/1 var(--serif);font-weight:600;letter-spacing:0;display:block}.brand:hover{color:var(--accent)}.brand span{display:block;font:8px/1 ui-monospace,SFMono-Regular,Menlo,monospace;letter-spacing:.16em;font-weight:400;color:var(--muted);margin-top:7px}.brand-divider{width:1px;height:34px;background:var(--line);flex:none}.site-label{font-size:11px;letter-spacing:2px;color:var(--muted);text-decoration:none;white-space:nowrap}.site-label:hover{color:var(--ink)}.edition{font-size:12px;color:var(--muted);letter-spacing:2px}.shell{max-width:1440px;margin:auto;display:grid;grid-template-columns:240px minmax(0,1fr);gap:5vw;padding:40px 5vw 75px}aside{min-width:0}.side-title{color:var(--muted);font-size:12px;letter-spacing:2px;display:flex;justify-content:space-between;padding:0 0 14px;border-bottom:1px solid var(--line)}nav a{display:flex;gap:13px;align-items:center;text-decoration:none;color:var(--ink);padding:16px 0;border-bottom:1px solid var(--line);font-size:14px}nav a[aria-current]{color:var(--accent);font-weight:600}nav .num{font:18px Georgia,serif;color:var(--muted)}nav .nav-status{margin-left:auto;font-size:12px;white-space:nowrap}.tools{display:grid;grid-template-columns:1fr 1fr;gap:8px;margin-top:32px}.tools button,.tools label{font-size:12px;padding:8px}.file-button{position:relative;overflow:hidden}.file-button input{position:absolute;inset:0;width:100%;height:100%;opacity:0;cursor:pointer}.file-button:focus-within{outline:3px solid var(--accent);outline-offset:3px}.muted,#message{color:var(--muted);font-size:12px}main{min-width:0;max-width:900px}main:focus{outline:none}.eyebrow{color:var(--accent);font-size:11px;letter-spacing:3px;text-transform:uppercase;margin:0 0 16px}h1{font:clamp(34px,5vw,64px)/1.25 var(--serif);font-weight:500;letter-spacing:-1px;margin:0 0 24px;max-width:780px}h2{font:26px/1.5 var(--serif);margin:0 0 18px;font-weight:500}h3{font-size:17px;margin:12px 0}.intro{font-size:17px;max-width:650px;color:var(--muted)}.hero{padding:22px 0 35px}.hero-meta{display:flex;gap:22px;flex-wrap:wrap;color:var(--muted);font-size:12px;letter-spacing:1px;margin:26px 0}.hero-art{width:100%;height:auto;display:block;border:1px solid var(--line);margin-top:24px}.goals{background:var(--panel);border-left:3px solid var(--accent);padding:24px;margin:24px 0 38px}.goals ul{margin:0;padding-left:22px}.progress-heading{display:flex;justify-content:space-between;gap:12px;align-items:center;font-size:13px}progress{width:100%;height:5px;accent-color:var(--accent);border:0;display:block;margin:14px 0 28px}progress::-webkit-progress-bar{background:var(--line)}progress::-webkit-progress-value{background:var(--accent)}.lesson-card{display:grid;grid-template-columns:45px minmax(0,1fr) auto;gap:15px;align-items:center;padding:23px 0;border-top:1px solid var(--line)}.lesson-card .number{font:28px Georgia,serif;color:var(--muted)}.lesson-card h3{margin:0}.lesson-card p{font-size:13px;color:var(--muted);margin:5px 0}.lesson-card a{white-space:nowrap;font-size:14px}.resume{padding:21px 24px;border:1px solid var(--accent);background:var(--tint);margin-bottom:24px}.resume p{margin:0 0 14px}.resume button+button{margin-left:8px}.lesson-head{padding:20px 0 30px;border-bottom:1px solid var(--line)}.section{padding:32px 0;border-bottom:1px solid var(--line)}.section-heading{display:flex;align-items:baseline;gap:15px}.section-heading span{font:12px Georgia,serif;color:var(--accent)}.conclusion{font:24px/1.8 var(--serif);background:var(--tint);padding:22px 26px}.block{margin:20px 0}.block p{margin:12px 0}.block ul{padding-left:24px}figure{margin:20px 0}figure img,video{max-width:100%;height:auto;display:block;border-radius:3px}figcaption{color:var(--muted);font-size:12px;margin-top:9px}audio{width:100%;max-width:100%}iframe{display:block;width:100%;max-width:100%;border:1px solid var(--line);background:var(--panel)}.code-wrap{position:relative;background:var(--code);color:var(--code-ink);padding:48px 20px 20px;border-radius:3px;margin:20px 0}.code-wrap pre{overflow:auto;margin:0;font:13px/1.8 "SFMono-Regular",Consolas,monospace;max-width:100%;tab-size:2}.copy{position:absolute;right:10px;top:8px;color:var(--code-ink);font-size:11px;padding:3px 12px;min-height:30px}.step{display:flex;align-items:flex-start;gap:12px;padding:16px;background:var(--panel);margin:10px 0}.step input,.option input,.complete input{accent-color:var(--accent);width:19px;height:19px;flex-shrink:0;margin:5px 0}.step>div{min-width:0}.step label{cursor:pointer}.step .block{margin:10px 0 0}.question{min-width:0;border:0;padding:0;margin:24px 0 34px}.question legend{font-weight:600;margin-bottom:10px}.option{display:flex;gap:12px;border:1px solid var(--line);padding:12px 16px;margin:8px 0;cursor:pointer}.option:has(input:checked){background:var(--tint);border-color:var(--accent)}.feedback{color:var(--accent);padding:14px 18px;border-left:2px solid var(--accent);background:var(--tint);margin-top:12px}.score{font-size:13px;color:var(--muted)}.complete{display:flex;gap:12px;align-items:center;font-weight:600;padding:24px 0;cursor:pointer}.lesson-footer{display:flex;justify-content:space-between;gap:16px;flex-wrap:wrap;padding:20px 0}.pitfall{background:var(--panel);padding:16px 22px;margin:12px 0}.pitfall p{margin:6px 0}footer{border-top:1px solid var(--line);padding:22px 5vw;display:flex;justify-content:space-between;font-size:10px;letter-spacing:2px;color:var(--muted);gap:16px}footer a{color:var(--muted);text-decoration:none;border-bottom:1px solid var(--line)}footer a:hover{color:var(--ink)}.skip{position:absolute;left:20px;top:-100px;background:var(--panel);padding:10px;z-index:5}.skip:focus{top:5px}.manual-copy{width:100%;min-height:120px} [hidden]{display:none!important}
@media(max-width:760px){.topbar{padding:20px 6vw}.brand-row{gap:12px}.brand{font-size:21px}.brand-divider{height:30px}.site-label{font-size:10px;letter-spacing:1.5px}.edition{display:none}.shell{display:flex;flex-direction:column;padding:25px 6vw 45px;gap:28px}aside{width:100%}nav{display:flex;gap:20px;flex-wrap:wrap}nav a{flex:1;min-width:130px;font-size:12px;padding:12px 0}.tools{display:flex;gap:6px;flex-wrap:wrap;margin-top:18px}.tools button,.tools label{flex:1;min-width:76px}.side-title{padding-bottom:8px}#storage-note{margin:8px 0 0}.hero{padding-top:0}h1{font-size:38px}.hero-meta{margin:18px 0}.lesson-card{grid-template-columns:30px minmax(0,1fr);gap:10px}.lesson-card a{grid-column:2}.section{padding:26px 0}.conclusion{font-size:21px;padding:18px}.resume{padding:18px}.goals{padding:18px}.lesson-head{padding-top:0}.section-heading h2{font-size:23px}footer{font-size:9px;letter-spacing:1px;flex-wrap:wrap}}
@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}}
/* Keep lesson numbers intact on narrow navigation rows. */
nav .num{flex-shrink:0;white-space:nowrap}