.stack-app{--paper:var(--card-background);--surface:var(--card-background);--ink:var(--card-text-color-main);--muted:var(--card-text-color-secondary);--line:var(--card-separator-color);--accent:var(--accent-color);--green:#385c45;--wash:#e9eddf;--side:245px;--serif:'Noto Serif SC','Source Han Serif SC','Songti SC',SimSun,serif;--sans:'Microsoft YaHei','PingFang SC','Noto Sans CJK SC',sans-serif;color-scheme:light}
    .stack-app *{box-sizing:border-box}.stack-app{scroll-behavior:smooth;scroll-padding-top:22px}.stack-app{color:inherit;background:var(--card-background);font-family:var(--base-font-family);line-height:1.75}.stack-app button,
.stack-app input{font-family:var(--base-font-family)}.stack-app a{color:inherit;text-decoration:none}.stack-app button{color:inherit;cursor:pointer}.stack-app button,
.stack-app a,
.stack-app input,
.stack-app summary{-webkit-tap-highlight-color:transparent}.stack-app button:focus-visible,
.stack-app a:focus-visible,
.stack-app input:focus-visible,
.stack-app summary:focus-visible{outline:3px solid var(--accent);outline-offset:4px}.stack-app [hidden]{display:none!important}.stack-app ::selection{background:var(--card-background)}.stack-app .skip{position:fixed;left:20px;top:-80px;z-index:10;padding:10px 20px;background:var(--card-background);color:inherit}.stack-app .skip:focus{top:12px}
    .stack-app .sidebar{position:fixed;inset:0 auto 0 0;width:var(--side);padding:39px 25px 26px;border-right:1px solid var(--card-separator-color);display:flex;flex-direction:column;background:var(--card-background);z-index:2}.stack-app .wordmark{font-family:var(--base-font-family);letter-spacing:.04em}.stack-app .wordmark span{font-weight:400;color:inherit}.stack-app .brand-mark{width:30px;height:29px;display:flex;gap:4px;margin-bottom:17px;align-items:flex-end}.stack-app .brand-mark i{display:block;width:6px;height:23px;background:var(--card-background)}.stack-app .brand-mark i:nth-child(2){height:28px;background:var(--card-background)}.stack-app .brand-mark i:nth-child(3){height:21px;transform:rotate(-13deg);transform-origin:bottom}.stack-app .sidebar-kicker{font-size:11px;color:inherit;letter-spacing:.18em;margin:9px 0 40px}.stack-app .nav-label{color:inherit;font-size:11px;letter-spacing:.13em;margin:0 12px 10px}.stack-app .subject{border:0;background:none;width:100%;display:flex;justify-content:space-between;align-items:center;text-align:left;padding:12px 13px;margin:2px 0;font-size:13px;border-radius:var(--card-border-radius);transition:background .18s,color .18s}.stack-app .subject:hover{background:var(--card-background)}.stack-app .subject[aria-pressed=true]{background:var(--card-background);color:inherit}.stack-app .nav-count{font-family:var(--base-font-family);opacity:.7}.stack-app .subject-all{margin-bottom:14px}.stack-app .sidebar-bottom{margin-top:auto;border-top:1px solid var(--card-separator-color);padding:20px 12px 0;font-size:11px;color:inherit}.stack-app .sidebar-bottom p{margin:0 0 6px}.stack-app .small-square{display:inline-block;width:6px;height:6px;background:var(--card-background);margin-right:6px}
    .stack-app main{margin-left:var(--side);padding:34px clamp(30px,5vw,86px) 44px;max-width:1580px}.stack-app .topline{display:flex;justify-content:space-between;gap:20px;color:inherit;font-size:11px;letter-spacing:.08em;padding-bottom:21px;border-bottom:1px solid var(--card-separator-color)}.stack-app .topline a:hover{color:inherit}.stack-app .hero{padding:50px 0 35px;position:relative}.stack-app .eyebrow{font-size:10px;letter-spacing:.16em;color:inherit;margin:0 0 9px}.stack-app .hero-eyebrow{color:inherit;letter-spacing:.2em;font-size:11px}.stack-app .hero h1{font-family:var(--base-font-family);letter-spacing:.045em;margin:16px 0 19px}.stack-app .hero h1 span{color:inherit;font-size:.75em;margin-left:9px}.stack-app .hero-copy{color:inherit;font-size:14px;line-height:2;margin:0;max-width:630px}.stack-app .hero-side{position:absolute;right:0;bottom:44px;width:80px;height:80px;border:1px solid var(--card-separator-color);border-radius:50%;display:grid;place-items:center;transform:rotate(-12deg);font-family:var(--base-font-family);text-align:center;color:inherit;letter-spacing:.15em}.stack-app .stats{display:flex;gap:42px;padding:23px 0;border-top:1px solid var(--card-separator-color);border-bottom:1px solid var(--card-separator-color);align-items:center}.stack-app .stat{display:flex;gap:10px;align-items:baseline}.stack-app .stat strong{font-family:var(--base-font-family)}.stack-app .stat span{color:inherit;font-size:12px}.stack-app .stats-note{margin-left:auto;font-size:11px;color:inherit;text-align:right}
    .stack-app .toolbar{display:flex;gap:20px;justify-content:space-between;align-items:center;padding:29px 0 24px}.stack-app .search{display:flex;align-items:center;gap:11px;max-width:440px;flex:1;background:var(--card-background);border:1px solid var(--card-separator-color);border-radius:var(--card-border-radius);padding:0 14px;min-width:0}.stack-app .search:focus-within{border-color:var(--card-separator-color);box-shadow:var(--shadow-l1)}.stack-app .search svg{width:17px;height:17px;flex:none;color:var(--muted)}.stack-app .search input{width:100%;min-width:0;background:none;border:0;outline:none!important;padding:12px 0;font-size:13px;color:inherit}.stack-app .search input::placeholder{color:inherit}.stack-app .key{border:1px solid var(--card-separator-color);border-radius:var(--card-border-radius);font-family:var(--base-font-family);width:20px;text-align:center;color:inherit}.stack-app .clear-search{border:0;padding:4px 0;background:none;font-size:12px;white-space:nowrap;color:inherit}.stack-app .toolbar-end{display:flex;gap:18px;align-items:center;white-space:nowrap}.stack-app .results{font-size:12px;color:inherit}.stack-app .expand{background:none;border:0;border-bottom:1px solid var(--card-separator-color);padding:3px 0;font-size:12px;white-space:nowrap}.stack-app .expand:hover{color:inherit;border-color:var(--card-separator-color)}
    .stack-app .course{background:var(--card-background);border:1px solid var(--card-separator-color);border-radius:var(--card-border-radius);margin-bottom:24px;padding:29px 31px 18px;animation:arrive .45s both}.stack-app .course-top{display:grid;grid-template-columns:45px minmax(0,1fr) auto;gap:18px}.stack-app .course-number{font-family:var(--base-font-family);color:inherit;padding-top:1px}.stack-app .course-heading .eyebrow{font-size:9px;letter-spacing:.12em;margin-bottom:7px}.stack-app .course h2{font-family:var(--base-font-family);letter-spacing:.015em;margin:0 0 10px}.stack-app .course-description{font-size:12px;line-height:1.95;color:inherit;margin:0;max-width:640px}.stack-app .tags{display:flex;gap:0;flex-wrap:wrap;color:inherit;font-size:10px;margin-top:13px;line-height:1.8}.stack-app .tags span+span:before{content:' / ';color:inherit;padding:0 10px}.stack-app .course-scope{text-align:right;font-size:11px;color:inherit;display:flex;flex-direction:column;gap:4px;min-width:96px}.stack-app .course-scope span:first-child{color:inherit}.stack-app .course-actions{margin:19px 0 19px 63px;display:flex;gap:22px;align-items:center;flex-wrap:wrap}.stack-app .read-link{background:var(--card-background);color:inherit;border-radius:var(--card-border-radius);padding:7px 15px;font-size:11px;display:inline-flex;align-items:center;gap:20px;transition:background .18s}.stack-app .read-link:hover{background:var(--card-background)}.stack-app .text-link{font-size:11px;color:inherit;text-decoration:underline;text-decoration-color:#c7d1bf;text-underline-offset:4px}.stack-app .text-link span{margin-left:6px}.stack-app .text-link:hover{color:inherit;text-decoration-color:var(--accent)}.stack-app .chapters{margin-left:63px}.stack-app .chapter{border-top:1px solid var(--card-separator-color)}.stack-app .chapter summary{display:flex;gap:10px;align-items:center;list-style:none;padding:13px 1px;cursor:pointer;font-size:12px;line-height:1.8}.stack-app .chapter summary::-webkit-details-marker{display:none}.stack-app .chapter summary:hover .chapter-name{color:inherit}.stack-app .chapter-name{flex:1}.stack-app .chapter-count{color:inherit;font-size:10px;white-space:nowrap}.stack-app .chevron{font-size:15px;line-height:1;color:inherit;width:19px;text-align:right;transition:transform .16s}.stack-app .chapter[open] .chevron{transform:rotate(45deg)}.stack-app .chapter-content{padding:0 0 10px}.stack-app .group-actions{display:flex;gap:22px;padding:0 0 12px 1px}.stack-app .lesson-list{margin:0;padding:0;list-style:none}.stack-app .lesson a{display:flex;align-items:baseline;gap:13px;padding:11px 10px;border-radius:var(--card-border-radius);font-size:12px;line-height:1.8;transition:background .16s}.stack-app .lesson a:hover{background:var(--card-background)}.stack-app .lesson-number{font-family:var(--base-font-family);color:inherit;min-width:27px}.stack-app .lesson-title{flex:1;overflow-wrap:anywhere}.stack-app .format{font-size:8px;letter-spacing:.05em;color:inherit;border:1px solid var(--card-separator-color);border-radius:var(--card-border-radius);padding:0 5px;white-space:nowrap}.stack-app .lesson-arrow{font-size:12px;color:inherit}.stack-app .plain-group{border-top:1px solid var(--card-separator-color);padding-top:6px}.stack-app .empty{text-align:center;padding:70px 20px;background:var(--card-background);border:1px solid var(--card-separator-color);border-radius:var(--card-border-radius)}.stack-app .empty h2{font-family:var(--base-font-family);margin:0 0 14px}.stack-app .empty p{font-size:13px;color:inherit;margin:0 0 22px}.stack-app .reset{padding:9px 18px;border:1px solid var(--card-separator-color);background:none;border-radius:var(--card-border-radius)}.stack-app .footer{border-top:1px solid var(--card-separator-color);display:flex;gap:24px;justify-content:space-between;align-items:flex-start;padding-top:22px;color:inherit;font-size:11px;margin-top:30px}.stack-app .footer p{margin:0;max-width:640px}.stack-app .footer a{white-space:nowrap;color:inherit}.stack-app .noscript{padding:12px 15px;background:var(--card-background);font-size:12px;margin-bottom:20px}.stack-app .mobile-caption{display:none}@keyframes arrive{from{opacity:0;transform:translateY(8px)}to{opacity:1;transform:translateY(0)}}
    @media(min-width:1600px){.stack-app{--side:270px}.stack-app .sidebar{padding-left:35px;padding-right:35px}.stack-app main{padding-left:78px;padding-right:78px}}
    @media(max-width:1100px){.stack-app{--side:210px}.stack-app .sidebar{padding:32px 18px}.stack-app .hero-side{display:none}.stack-app .course-top{grid-template-columns:36px minmax(0,1fr);gap:13px}.stack-app .course-scope{grid-column:2;text-align:left;flex-direction:row;gap:15px;margin-top:-4px}.stack-app .course-actions,
.stack-app .chapters{margin-left:49px}.stack-app .course{padding:25px 23px 15px}.stack-app .stats{gap:30px}.stack-app .stats-note{display:none}.stack-app .toolbar-end{gap:12px}}
    @media(max-width:760px){.stack-app{--side:0px}.stack-app .sidebar{position:static;width:auto;padding:22px 21px 0;border-right:0}.stack-app .brand{display:flex;align-items:center;gap:10px}.stack-app .brand-mark{width:20px;height:22px;margin:0;gap:3px}.stack-app .brand-mark i{width:4px;height:16px}.stack-app .brand-mark i:nth-child(2){height:21px}.stack-app .brand-mark i:nth-child(3){height:16px}.stack-app .wordmark{font-size:14px}.stack-app .sidebar-kicker{margin:0 0 0 auto;font-size:9px;letter-spacing:.12em}.stack-app .nav-label,
.stack-app .sidebar-bottom{display:none}.stack-app .subject-nav{margin-top:22px;display:flex;gap:7px;overflow-x:auto;padding-bottom:12px;border-bottom:1px solid var(--card-separator-color);scrollbar-width:thin}.stack-app .subject{width:auto;flex:none;gap:16px;margin:0;padding:7px 12px;font-size:11px;border:1px solid var(--card-separator-color)}.stack-app .subject-all{margin:0}.stack-app .nav-count{font-size:10px}.stack-app main{padding:0 22px 30px;margin:0}.stack-app .topline{padding-top:16px;padding-bottom:0;border:0;font-size:9px}.stack-app .topline span:last-child{display:none}.stack-app .hero{padding:29px 0 24px}.stack-app .hero h1{font-size:43px;margin:12px 0 15px}.stack-app .hero-copy{font-size:12px;line-height:2}.stack-app .hero-eyebrow{font-size:9px}.stack-app .stats{gap:24px;padding:18px 0}.stack-app .stat{gap:7px}.stack-app .stat strong{font-size:25px}.stack-app .stat span{font-size:10px}.stack-app .toolbar{flex-wrap:wrap;gap:12px;padding:20px 0}.stack-app .search{max-width:none;flex-basis:100%}.stack-app .toolbar-end{width:100%;justify-content:space-between}.stack-app .course{padding:22px 17px 12px;margin-bottom:17px}.stack-app .course-top{grid-template-columns:28px minmax(0,1fr);gap:10px}.stack-app .course-number{font-size:25px}.stack-app .course h2{font-size:21px}.stack-app .course-description{font-size:11px}.stack-app .course-heading .eyebrow{font-size:8px;letter-spacing:.09em}.stack-app .course-scope{font-size:10px;gap:12px}.stack-app .tags{font-size:9px}.stack-app .tags span+span:before{padding:0 6px}.stack-app .course-actions{margin:18px 0;gap:18px}.stack-app .chapters{margin-left:0}.stack-app .chapter summary{padding:13px 0;font-size:11px}.stack-app .lesson a{padding:10px 2px;gap:9px;font-size:11px}.stack-app .lesson-number{min-width:25px}.stack-app .lesson-arrow{display:none}.stack-app .footer{font-size:10px;gap:14px}.stack-app .footer p{max-width:80%}.stack-app .key{display:none}}
    @media(prefers-reduced-motion:reduce){.stack-app{scroll-behavior:auto}.stack-app .course{animation:none}.stack-app *{transition:none!important}}
    @media print{.stack-app .sidebar,
.stack-app .toolbar,
.stack-app .hero-side,
.stack-app .topline,
.stack-app .course-actions,
.stack-app .footer a{display:none}.stack-app main{margin:0;padding:0}.stack-app .course{break-inside:avoid;animation:none}.stack-app .hero{padding-top:0}.stack-app .course{background:var(--card-background)}.stack-app{background:var(--card-background)}.stack-app .stats{padding:12px 0}.stack-app .course h2{font-size:20px}.stack-app .lesson a{padding:5px 0}}
    .stack-app .subject-nav{overflow-y:auto;min-height:0}.stack-app .course-description{font-size:14px}.stack-app .chapter summary,
.stack-app .lesson a{font-size:13px}
    @media(max-width:760px){.stack-app .subject-nav{overflow-y:hidden}}
    @media(max-width:760px){.stack-app .course-description,
.stack-app .chapter summary,
.stack-app .lesson a,
.stack-app .hero-copy{font-size:13px}}