:root{--subject-bg:#f6f6f6;--subject-card:#fff;--subject-text:#202020;--subject-muted:#626262;--subject-line:#d8d8d8;--subject-hover:#ededed}
html[data-theme=dark]{--subject-bg:#111;--subject-card:#1b1b1b;--subject-text:#eee;--subject-muted:#bbb;--subject-line:#414141;--subject-hover:#303030}
#subject-navigation{background:var(--subject-card);border-bottom:1px solid var(--subject-line);color:var(--subject-text)}.subject-bar-inner{max-width:1440px;margin:auto;display:flex;gap:40px;align-items:center;padding:20px 24px}.subject-brand{display:flex;align-items:center;gap:12px;color:inherit;text-decoration:none;font:600 26px Georgia,serif;white-space:nowrap}.subject-brand>span{border:1px solid var(--subject-line);border-radius:9px;width:39px;height:39px;display:grid;place-items:center;font-size:28px}.subject-bar-inner nav{display:flex;align-items:center;gap:6px;flex-wrap:wrap}.subject-bar-inner nav a{padding:11px 15px;text-decoration:none;border-radius:8px;font-size:14px;font-weight:500;color:var(--subject-muted)}.subject-bar-inner nav a:hover{background:var(--subject-hover);color:var(--subject-text)}.subject-bar-inner nav a[aria-current=page]{background:var(--subject-text);color:var(--subject-card)}
#subject-home{max-width:1440px;margin:0 auto;padding:45px 24px;background:var(--subject-bg);color:var(--subject-text);min-height:calc(100vh - 80px)}body:has(#subject-home:not([hidden])){background:var(--subject-bg)}.subject-home-top{display:flex;gap:20px;align-items:flex-start;justify-content:space-between;margin-bottom:34px}.subject-eyebrow{font-size:12px!important;letter-spacing:.14em;margin-bottom:14px!important;font-weight:600;color:var(--subject-muted)}.subject-home-top h1{font:400 clamp(30px,3vw,44px)/1.2 Georgia,serif;margin-bottom:14px}.subject-home-top p{font-size:16px;line-height:1.6;color:var(--subject-muted)}.subject-home-settings{display:flex;gap:8px}.subject-home-settings button{background:var(--subject-card);color:var(--subject-text);border:1px solid var(--subject-line);border-radius:8px;padding:10px;min-height:44px;min-width:44px}.subject-cards{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:20px}.subject-card{background:var(--subject-card);border:1px solid var(--subject-line);border-radius:14px;padding:26px;display:flex;flex-direction:column;min-width:0}.subject-symbol{font:28px Georgia,serif;margin-bottom:20px;height:34px}.subject-card h2{font-size:23px;line-height:1.3;margin:0 0 14px;min-height:60px}.subject-card h2 a{color:inherit;text-decoration:none}.subject-card>p{font-size:16px;line-height:1.6;color:var(--subject-muted);min-height:76px}.subject-card ul{list-style:none;padding:0;margin:20px 0 28px}.subject-card li{border-top:1px solid var(--subject-line)}.subject-card li a{display:flex;justify-content:space-between;align-items:center;gap:12px;text-decoration:none;color:var(--subject-text);padding:13px 0;font-size:14px;line-height:1.5;min-height:49px}.subject-card li a:hover{text-decoration:underline}.subject-card li span{color:var(--subject-muted)}.subject-start{display:flex;justify-content:space-between;margin-top:auto;padding:12px 15px;min-height:44px;background:var(--subject-text);color:var(--subject-card);border-radius:8px;text-decoration:none;font-size:14px;font-weight:600}.subject-home-note{margin-top:25px;font-size:14px;line-height:1.7;color:var(--subject-muted);max-width:850px}
/* Subject-specific tools share the same primary navigation and content frame. */
#app{max-width:1440px;margin:0 auto;min-height:calc(100vh - 80px);padding:24px;gap:24px;background:var(--subject-bg)}#app .sidebar{position:static;inset:auto;width:225px;padding:0;align-self:flex-start;overflow:visible;background:transparent;color:var(--subject-text);border:0}#app .sidebar :is(.brand,.course-label,.sidebar-note,.sidebar-bottom){display:none}#app .sidebar .nav-label{margin:0 0 12px;color:var(--subject-muted);font-size:12px}#app .sidebar nav{display:block;overflow:visible}#app .topic{background:var(--subject-card);border:1px solid var(--subject-line);color:var(--subject-text);margin-bottom:8px;width:100%;padding:12px;min-height:60px;flex-shrink:1}#app .topic strong{font-size:14px}#app .topic small{font-size:12px;color:var(--subject-muted)}#app .topic.active{background:var(--subject-text);color:var(--subject-card)}#app .topic.active small{color:var(--subject-card);opacity:.8}#app .topic .active-dot{display:none}#app .main{margin:0;width:calc(100% - 249px);background:var(--subject-bg)}#app main{padding:24px 0 0;max-width:none;margin:0}#app .topbar{padding:0 0 18px;background:transparent;min-height:60px;gap:12px}#app .intro{margin-bottom:25px}#app .intro h1{font-size:36px}#app .intro .eyebrow{display:none}#app .intro .practice-stat{font-size:12px}#app .intro p{font-size:16px}#app footer{font-size:12px}#app .avatar{display:none}
#course-root .course-shell{min-height:calc(100vh - 80px);max-width:1440px;margin:auto;padding:24px;background:var(--subject-bg)}#course-root .course-title{padding:24px 0}#course-root .course-title h1{font:400 36px/1.2 Georgia,serif}#course-root .course-title>span{display:none}#course-root .course-main{background:transparent}#course-root .course-header{padding-bottom:18px;min-height:60px}html[data-theme=dark] #course-root .course-shell button{background:var(--c-card);color:var(--c-text);border-color:var(--c-line)}html[data-theme=dark] #course-root .course-shell :is(.primary,.selected){background:var(--c-text);color:var(--c-card)}
@media(max-width:1000px){.subject-bar-inner{gap:20px}.subject-cards{gap:14px}.subject-card{padding:20px}.subject-card h2{font-size:21px}.subject-card>p{min-height:100px}#app .sidebar{width:195px}#app .main{width:calc(100% - 219px)}}
@media(max-width:760px){.subject-bar-inner{flex-direction:column;align-items:stretch;padding:15px 16px;gap:14px}.subject-bar-inner nav{display:grid;grid-template-columns:1fr 1fr;gap:6px}.subject-bar-inner nav a{font-size:14px;text-align:center;padding:10px 8px;display:grid;place-items:center;border:1px solid var(--subject-line);min-height:44px}.subject-brand{font-size:24px}.subject-brand>span{height:34px;width:34px}.subject-cards{grid-template-columns:1fr}.subject-card h2,.subject-card>p{min-height:0}.subject-card h2{font-size:24px}.subject-card li a{font-size:16px}.subject-home-top{flex-direction:column-reverse;gap:18px}.subject-home-settings{align-self:flex-end}#subject-home{padding:22px 16px}.subject-home-top h1{font-size:32px}.subject-card{padding:22px}.subject-symbol{margin-bottom:12px}.subject-card ul{margin-top:18px}#app{display:block;padding:20px 16px}#app .sidebar{width:100%;padding:0}#app .sidebar nav{display:grid;grid-template-columns:1fr 1fr;gap:8px}#app .topic{margin:0;padding:10px;min-height:70px;gap:7px}#app .topic strong{font-size:13px}#app .topic small{font-size:12px}#app .topic-symbol{font-size:18px;width:20px}#app .main{width:100%;margin-top:22px}#app .topbar{padding-bottom:15px}#app .intro h1{font-size:32px}#app .intro{gap:15px}#app .intro .practice-stat{display:none}#course-root .course-shell{padding:20px 16px}#course-root .course-title h1{font-size:32px}}
@media print{#subject-navigation,#subject-home{display:none!important}#app{display:block;padding:0}#app .main{width:100%}}
#app .reference-tabs{flex-wrap:wrap;gap:8px}#app .reference-tabs button{flex:1 1 auto;white-space:normal;line-height:1.4;padding:8px 4px 12px}

.row-walk{border-top:1px solid var(--subject-line);margin-top:24px;padding-top:18px;color:var(--subject-text)}.row-walk p{font-size:14px;line-height:1.6;margin:10px 0}.row-equation{display:block;font-size:18px;overflow-wrap:anywhere;padding:12px;border:1px solid var(--subject-line);border-radius:8px}.row-walk-cells{display:flex;flex-wrap:wrap;gap:8px;margin:16px 0}.row-walk-cells span{padding:10px;min-width:40px;border:1px solid var(--subject-line);border-radius:6px;overflow-wrap:anywhere;max-width:100%}.row-walk-cells .walk-active{background:var(--subject-text);color:var(--subject-card);animation:walk-in .3s ease-out}@keyframes walk-in{from{transform:translateY(-5px);opacity:.4}to{transform:translateY(0);opacity:1}}@media(prefers-reduced-motion:reduce){.row-walk-cells .walk-active{animation:none}}