:root{--bg:#f8f7f3;--paper:#fffefa;--sidebar:#f0efea;--text:#303638;--muted:#63696b;--line:#deded6;--accent:#80515a;--accent-hover:#68414a;--tint:#f0e6e6;--green:#3d6b57;--sans:-apple-system,BlinkMacSystemFont,'Segoe UI',sans-serif;--serif:Georgia,'Times New Roman',serif;color-scheme:light}
:root[data-theme=dark]{--bg:#202426;--paper:#282e30;--sidebar:#1d2224;--text:#edece7;--muted:#b3babc;--line:#424a4c;--accent:#dbabb4;--accent-hover:#edc1ca;--tint:#413138;--green:#aad0b8;color-scheme:dark}
*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;background:var(--bg);color:var(--text);font:15px/1.7 var(--sans);-webkit-font-smoothing:antialiased}a{color:inherit;text-decoration:none}button,input,select,textarea{font:inherit;color:inherit}button,a,input,select,summary{touch-action:manipulation}button{cursor:pointer}button:disabled{cursor:default;opacity:.65}button,a,input,select,textarea,summary{outline-offset:4px}button:focus-visible,a:focus-visible,input:focus-visible,select:focus-visible,textarea:focus-visible,summary:focus-visible{outline:3px solid var(--accent)}h1,h2,h3,p{margin-top:0}h1{font:400 clamp(36px,4.6vw,60px)/1.13 var(--serif);letter-spacing:-1.7px;margin-bottom:23px}h2{font:400 29px/1.25 var(--serif);letter-spacing:-.6px}h3{font-size:17px;line-height:1.4}p{margin-bottom:16px}small{font-size:12px}.muted{color:var(--muted);font-size:13px}.skip{position:fixed;left:20px;top:-100px;z-index:100;background:var(--paper);padding:12px 20px;border:1px solid var(--accent);border-radius:12px}.skip:focus{top:10px}
.sidebar{position:fixed;inset:0 auto 0 0;width:238px;padding:30px 18px;background:var(--sidebar);border-right:1px solid var(--line);overflow:auto;z-index:20}.brand{display:flex;align-items:center;gap:12px;margin:0 12px 34px;font-size:24px;font-weight:600;line-height:1.3}.brand-mark{display:grid;place-items:center;background:var(--accent);color:var(--paper);font:italic 31px var(--serif);width:42px;height:42px;border-radius:13px}.brand small{display:block;font-size:11px;font-weight:400;color:var(--muted);margin-top:2px}.nav-label{font-size:9px;font-weight:650;letter-spacing:1.1px;color:var(--muted);margin:25px 12px 10px}.nav-item{display:flex;align-items:center;gap:13px;padding:10px 13px;min-height:44px;border-radius:12px;color:var(--muted);font-size:13px;margin:3px 0}.nav-item>span{font-size:17px;min-width:20px}.nav-item.active,.nav-item:hover{background:var(--paper);color:var(--accent)}#topics-nav>a{display:flex;align-items:center;gap:10px;padding:8px 13px;min-height:44px;font-size:11px;line-height:1.45;border-radius:10px;color:var(--muted)}#topics-nav>a>span{font:11px ui-monospace,monospace;color:var(--accent);flex-shrink:0}#topics-nav>a>i{margin-left:auto;font-style:normal;color:var(--green)}#topics-nav>a:hover,#topics-nav>a[aria-current]{background:var(--paper);color:var(--text)}.sidebar-bottom{margin:28px 12px 0;padding-top:20px;border-top:1px solid var(--line);font-size:11px;color:var(--muted)}.progress-track{height:4px;background:var(--line);border-radius:5px;margin:11px 0 14px}.progress-track>div{height:100%;background:var(--accent);border-radius:5px;transition:width .2s}.sidebar-bottom small{font-size:10px}
.workspace{margin-left:238px}.topbar{min-height:77px;border-bottom:1px solid var(--line);display:flex;align-items:center;justify-content:space-between;padding:14px 40px;gap:20px;font-size:12px;color:var(--muted)}.top-tools{display:flex;align-items:center;gap:19px}.icon-button{border:1px solid var(--line);border-radius:12px;min-width:44px;height:44px;background:transparent;font-size:20px}.mobile-brand{display:none}.network{display:flex;gap:24px;align-items:center;padding:0 40px;min-height:51px;border-bottom:1px solid var(--line);font-size:11px;overflow-x:auto;white-space:nowrap}.network a{display:flex;align-items:center;min-height:48px;color:var(--muted)}.network a:hover,.network a[aria-current]{color:var(--accent)}.network a:first-child{font-weight:650}.mobile-nav{display:none}main{max-width:1240px;margin:auto;padding:40px 46px 66px;min-height:70vh}footer{display:flex;justify-content:space-between;gap:20px;flex-wrap:wrap;border-top:1px solid var(--line);padding:23px 40px;color:var(--muted);font-size:10px}footer a:hover{text-decoration:underline}
.eyebrow{font-size:10px;font-weight:600;letter-spacing:1.4px;color:var(--accent);display:block;margin-bottom:17px}.hero{padding:22px 0 42px;border-bottom:1px solid var(--line);margin-bottom:34px}.hero h1{max-width:680px}.hero p{color:var(--muted);font-size:15px;line-height:1.9}.actions{display:flex;flex-wrap:wrap;align-items:center;gap:13px 23px;margin:25px 0 12px}.button{border:1px solid var(--accent);background:var(--accent);color:var(--paper);font-size:12px;font-weight:550;min-height:46px;display:inline-flex;align-items:center;justify-content:center;gap:24px;border-radius:12px;padding:12px 21px;line-height:1.5}.button:hover{background:var(--accent-hover);border-color:var(--accent-hover)}.button.secondary{color:var(--accent);background:transparent;border-color:var(--line)}.button.secondary:hover{border-color:var(--accent);background:var(--tint)}.text-link{border:0;background:transparent;padding:9px 0;min-height:44px;display:inline-flex;align-items:center;gap:8px;color:var(--accent);font-size:12px;line-height:1.5;text-align:left}.text-link:hover{text-decoration:underline;text-underline-offset:4px}.next-line{font-size:11px;color:var(--muted);margin-top:17px}.section-heading{display:flex;align-items:baseline;justify-content:space-between;gap:20px;margin-bottom:22px}.section-heading h2{margin:0}.section-heading>.muted{font-size:11px}.topic-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:15px}.topic-card{background:var(--paper);border:1px solid var(--line);border-radius:16px;padding:24px 22px;display:flex;flex-direction:column;transition:border-color .2s,transform .2s;min-width:0}.topic-card:hover{border-color:var(--accent);transform:translateY(-2px)}.topic-card .eyebrow{font-size:9px;margin-bottom:20px}.topic-card h3{font:500 17px/1.4 var(--sans);margin-bottom:10px}.topic-card p{font-size:12px;color:var(--muted);line-height:1.8;flex:1}.card-bottom{display:flex;align-items:center;justify-content:space-between;gap:10px;font-size:10px;color:var(--muted);margin-top:15px;padding-top:14px;border-top:1px solid var(--line)}.card-bottom>span:last-child{color:var(--accent);font-size:18px}.note{padding:25px 28px;background:var(--paper);border:1px solid var(--line);border-radius:16px;margin:30px 0}.note p{font-size:13px;color:var(--muted);margin:10px 0 0}.note>strong{font-size:14px}.note h2{font-size:25px}.page-title{margin-bottom:32px}.page-title h1{font-size:clamp(34px,4vw,49px);margin-bottom:18px}.page-title p{max-width:740px;color:var(--muted);font-size:14px;line-height:1.9}
.lesson-layout{display:grid;grid-template-columns:minmax(0,1fr) 180px;gap:32px;align-items:start}.article{max-width:850px;min-width:0}.article-section{margin-bottom:42px;padding-bottom:34px;border-bottom:1px solid var(--line);scroll-margin-top:22px}.article-section h2{margin-bottom:20px}.article-section .eyebrow{font-size:11px}.prose,.article p,.article li{font-size:14px;line-height:1.95}.prose{white-space:pre-line}.example{margin:24px 0;padding:24px;background:var(--paper);border:1px solid var(--line);border-radius:14px;font-size:13px}.example>strong{display:block;font-size:10px;text-transform:uppercase;letter-spacing:1px;color:var(--accent);margin-bottom:12px}.trap{border-left:3px solid var(--accent);padding:5px 0 5px 18px;margin:24px 0;font-size:13px;color:var(--muted)}.trap strong{color:var(--accent);font-size:12px}.trap p{margin:6px 0;font-size:13px}.lesson-toc{position:sticky;top:20px;padding-left:18px;border-left:1px solid var(--line)}.lesson-toc .nav-label{margin:0 0 12px}.lesson-toc a{display:block;padding:10px 0;min-height:44px;font-size:11px;line-height:1.6;color:var(--muted)}.lesson-toc a:hover{color:var(--accent)}.lesson-pagination{display:flex;justify-content:space-between;gap:20px;border-top:1px solid var(--line);margin-top:35px;padding-top:20px;font-size:12px;color:var(--accent)}.lesson-pagination>a{max-width:48%;min-height:44px}.source-link{display:inline-block;min-height:44px;padding:12px 0;font-size:11px;color:var(--accent);margin-right:15px;line-height:1.6}.source-link:hover{text-decoration:underline}.note-label{display:block;font-size:12px;font-weight:550;margin-bottom:10px}textarea,input,select{background:var(--paper);border:1px solid var(--line);border-radius:12px;min-height:46px;padding:11px 13px;max-width:100%}textarea{width:100%;resize:vertical;font-size:14px}input{min-width:0}select{font-size:12px;max-width:100%;padding-right:26px}pre{font:12px/1.9 ui-monospace,SFMono-Regular,Consolas,monospace;white-space:pre;overflow-x:auto;max-width:100%;padding:23px;background:var(--sidebar);border:1px solid var(--line);border-radius:14px;color:var(--text);tab-size:4}code{font-family:inherit}
.toolbar{display:flex;gap:12px;flex-wrap:wrap;margin:0 0 25px}.search{flex:1;min-width:200px;width:100%;font-size:13px;margin-bottom:0}.formula-grid{display:grid;grid-template-columns:1fr 1fr;gap:16px;margin-top:25px}.formula-card{background:var(--paper);border:1px solid var(--line);border-radius:15px;padding:25px;min-width:0;margin-bottom:15px}.formula-card h2,.formula-card h3{font:550 15px/1.5 var(--sans);letter-spacing:0;margin-bottom:14px}.formula-card p{font-size:12px;color:var(--muted);line-height:1.9;margin:15px 0 0}.formula-card .eyebrow{font-size:9px}.math-inline{display:inline}.math-inline>.katex{font-size:1.06em;white-space:nowrap}.math-block{display:block;max-width:100%;overflow-x:auto;overflow-y:hidden;padding:15px 3px;margin:12px 0;overscroll-behavior-x:contain;white-space:normal;line-height:1.6}.math-block .katex-display{margin:0}.math-block .katex{font-size:1.1em}.question-title .math-block .katex{font-size:.85em}
.question-card,.lab-card,.setup{background:var(--paper);border:1px solid var(--line);border-radius:18px;padding:32px;margin-bottom:24px;min-width:0}.question-topic{font-size:11px;color:var(--accent);margin:0 0 20px}.question-title{font:500 20px/1.7 var(--sans);letter-spacing:-.3px;white-space:pre-line}.options{display:grid;gap:10px;margin:23px 0}.option{display:flex;align-items:center;gap:17px;border:1px solid var(--line);border-radius:12px;background:transparent;padding:16px 20px;min-height:56px;text-align:left;font-size:14px;line-height:1.8;min-width:0}.option>span:first-child{font:11px ui-monospace,monospace;color:var(--accent)}.option:hover,.option.selected{border-color:var(--accent);background:var(--tint)}.option>span:last-child{min-width:0}.numeric-row{display:flex;gap:12px;max-width:550px}.numeric-row>input{flex:1;min-width:0;width:100%}.feedback{padding:24px;border-radius:13px;background:var(--tint);margin:25px 0;font-size:13px;line-height:1.9}.feedback.correct{border-left:3px solid var(--green)}.feedback.wrong{border-left:3px solid var(--accent)}.feedback h3{font-size:16px;margin-bottom:12px}.feedback p{margin-bottom:12px}.steps{padding-left:22px}.steps li{padding:4px 0 10px}.error{color:var(--accent);font-size:13px;margin:12px 0}.empty{padding:40px 30px;text-align:center;border:1px dashed var(--line);border-radius:16px;color:var(--muted)}.empty h2{color:var(--text)}
.homework-list{display:grid;gap:16px}details>summary{cursor:pointer;min-height:44px;line-height:1.7}details[open]>summary{margin-bottom:18px}.homework-card{border:1px solid var(--line);border-radius:16px;background:var(--paper);padding:25px 28px;min-width:0}.homework-card>summary{list-style:none}.homework-card>summary::-webkit-details-marker{display:none}.homework-card>summary>h2{font:550 19px/1.5 var(--sans);letter-spacing:-.3px;margin-bottom:12px}.homework-card>summary>p{font-size:13px;color:var(--muted);margin-bottom:0;white-space:pre-line}.homework-content{border-top:1px solid var(--line);padding-top:24px;min-width:0}.guided-steps{list-style:none;padding:0;margin:0 0 25px}.guided-steps>li{padding:15px 0;border-bottom:1px solid var(--line);font-size:13px}.guided-steps summary{color:var(--accent);font-weight:500}.guided-steps details>div{white-space:pre-line;line-height:1.95}.check{display:flex;align-items:center;gap:10px;font-size:12px;color:var(--muted);min-height:44px;margin-top:12px}.check input{min-height:20px;width:19px;height:19px;accent-color:var(--accent)}.material-list{border:1px solid var(--line);border-radius:16px;overflow:hidden;background:var(--paper)}.material-item{display:flex;align-items:center;gap:18px;padding:19px 23px;border-bottom:1px solid var(--line);min-height:88px}.material-item:last-child{border:0}.material-item:hover{background:var(--tint)}.file-type{font:10px ui-monospace,monospace;color:var(--accent);border:1px solid var(--line);border-radius:8px;padding:8px;min-width:51px;text-align:center}.material-item>div{flex:1;min-width:0}.material-item h3{font-size:13px;margin:0 0 3px}.material-item p{font-size:10px;color:var(--muted);margin:0}.material-item>span:last-child{color:var(--accent)}
.tabs{display:flex;gap:8px;flex-wrap:wrap;margin:0 0 23px}.tabs>button{border:1px solid var(--line);border-radius:12px;padding:10px 15px;min-height:44px;background:transparent;color:var(--muted);font-size:12px}.tabs>button.active{background:var(--tint);border-color:var(--accent);color:var(--accent)}.lab-card>h2{font-size:27px}.lab-card>p{font-size:13px;color:var(--muted)}.fields{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:14px;margin:22px 0}.field{display:flex;flex-direction:column;gap:9px;font-size:12px}.field input{width:100%;font-size:14px}.field.wide{grid-column:1/-1}.field textarea{margin-bottom:4px}.metrics{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:18px;margin:28px 0}.metrics>div{padding:15px 18px;border:1px solid var(--line);border-radius:12px;background:var(--paper);min-width:0}.metrics dt{font-size:11px;color:var(--muted);margin-bottom:7px}.metrics dd{margin:0;color:var(--accent);font-size:21px;overflow-wrap:anywhere}.histogram{max-width:700px;margin:30px 0}.histogram svg{display:block;width:100%;height:auto}.histogram figcaption{font-size:10px;color:var(--muted);margin-top:10px}#lab-result>p{font-size:13px;color:var(--muted)}.exam-bar{display:flex;justify-content:space-between;align-items:center;gap:20px;padding:19px 24px;background:var(--tint);border:1px solid var(--line);border-radius:14px;margin-bottom:25px;font-size:13px}.exam-bar strong{font:23px ui-monospace,monospace;color:var(--accent)}.setup>p{color:var(--muted);font-size:14px}.setup .steps{font-size:13px}.plan-grid{display:grid;grid-template-columns:1fr 1fr;gap:18px}.plan-grid .note{margin:10px 0}.backup-panel{padding:27px;border:1px solid var(--line);border-radius:16px;background:var(--paper);margin-top:28px}.backup-panel p{font-size:13px;color:var(--muted)}.backup-panel h2{font-size:27px}.file-button{position:relative;cursor:pointer;overflow:hidden}.file-button input{position:absolute;inset:0;opacity:0;cursor:pointer;width:100%}.file-button:focus-within{outline:3px solid var(--accent);outline-offset:4px}.reset-panel{margin-top:28px;padding:20px 0;border-top:1px solid var(--line);color:var(--muted);font-size:12px}.reset-panel>p{margin-top:15px}#toast{position:fixed;bottom:25px;left:50%;transform:translate(-50%,20px);background:var(--text);color:var(--bg);padding:13px 23px;border-radius:12px;font-size:12px;opacity:0;pointer-events:none;transition:.2s;z-index:80;max-width:90vw;text-align:center}#toast.show{opacity:1;transform:translate(-50%,0)}
@media(min-width:1500px){main{padding-top:55px}.hero{padding-top:30px;padding-bottom:50px}.topic-card{padding:28px}.topic-grid{gap:20px}}
@media(max-width:1200px){.sidebar{width:215px;padding-inline:12px}.workspace{margin-left:215px}main{padding:32px}.topbar,.network{padding-inline:32px}.network{gap:20px}.topic-grid{grid-template-columns:1fr 1fr}.lesson-layout{grid-template-columns:minmax(0,1fr)}.lesson-toc{display:none}.brand{font-size:22px}}
@media(max-width:850px){.sidebar{display:none}.workspace{margin-left:0}.topbar{min-height:72px;padding:13px 24px}.topbar>#breadcrumb{display:none}.mobile-brand{display:block;font-size:14px;font-weight:550;color:var(--text)}#local-status{font-size:10px}.network{padding-inline:24px;font-size:10px;gap:22px;min-height:45px}.network a{min-height:44px}.mobile-nav{display:flex;padding:0 24px;gap:22px;overflow:auto;white-space:nowrap;border-bottom:1px solid var(--line);font-size:11px}.mobile-nav a{padding:12px 0;min-height:46px;color:var(--muted)}.mobile-nav a[aria-current]{color:var(--accent);border-bottom:2px solid var(--accent)}main{padding:32px 24px 50px}.hero{padding:10px 0 32px}.hero h1{font-size:48px}.hero p{font-size:14px}.question-card,.lab-card,.setup{padding:26px}.top-tools{gap:12px}footer{padding-inline:24px}}
@media(max-width:560px){body{font-size:14px}h1{letter-spacing:-1px}.hero h1{font-size:39px}.hero p br{display:none}.hero .actions{align-items:stretch;gap:6px}.hero .actions>.button{width:100%}.hero .actions>.text-link{justify-content:center;width:100%}.eyebrow{font-size:9px;letter-spacing:1px}.topic-grid{grid-template-columns:1fr;gap:12px}.topic-card{padding:22px}.topic-card p{margin-bottom:5px}.topic-card .eyebrow{margin-bottom:12px}.card-bottom{margin-top:10px}.section-heading h2{font-size:27px}.section-heading>.muted{display:none}main{padding:27px 20px 44px}.topbar{padding-inline:20px}.network,.mobile-nav{padding-inline:20px}#local-status{display:none}.page-title h1{font-size:35px}.page-title p{font-size:13px}.toolbar{gap:10px}.toolbar select{width:100%;min-width:0}.search{min-width:0}.formula-grid{grid-template-columns:1fr}.note{padding:22px}.question-card,.lab-card,.setup{padding:22px 18px}.question-title{font-size:18px}.option{padding:14px 13px;gap:12px;font-size:13px}.numeric-row{flex-wrap:wrap}.numeric-row>.button{width:100%}.numeric-row>input{flex-basis:100%}.feedback{padding:19px 16px}.metrics{gap:10px;grid-template-columns:1fr 1fr}.metrics>div{padding:13px 12px}.metrics dd{font-size:19px}.metrics dt{font-size:10px}.fields{grid-template-columns:1fr}.field.wide{grid-column:auto}.plan-grid{grid-template-columns:1fr}.homework-card{padding:23px 19px}.homework-card>summary>h2{font-size:17px}.material-item{padding:18px 14px;gap:12px}.material-item h3{font-size:12px}.material-item p{font-size:9px}.file-type{min-width:45px;font-size:9px;padding:7px}.exam-bar{padding:16px;flex-wrap:wrap}.exam-bar>.button{width:100%}.lesson-pagination{font-size:11px}.article-section h2{font-size:27px}.prose,.article p,.article li{font-size:13px}.math-block .katex{font-size:1em}pre{padding:18px;font-size:11px}.backup-panel{padding:22px 18px}.backup-panel .button{width:100%}.actions>.button{gap:10px}footer{padding:20px;font-size:9px}.steps{padding-left:19px}}
@media(prefers-reduced-motion:reduce){*{scroll-behavior:auto!important;transition:none!important}.topic-card:hover{transform:none}}@media print{.sidebar,.topbar,.network,.mobile-nav,footer,.lesson-toc,.actions,.toolbar,#toast{display:none!important}.workspace{margin:0}main{padding:0;max-width:none}.question-card,.article-section,.formula-card{break-inside:avoid}.math-block{overflow:visible}body{background:white;color:black}}

/* Native MathML keeps formula layout compatible with the shared strict CSP. */
.katex>math{font-family:math,'Cambria Math','STIX Two Math',serif;font-size:1em;line-height:normal}.math-block>.katex{display:block}.math-block math[display=block]{display:block;margin:0;text-align:center}.math-inline math{display:inline}.math-block math{max-width:none}.math-block .katex{white-space:normal}

/* Quiet, decorative markers: text labels carry the accessible meaning. */
.ui-emoji{display:inline-block;font-family:"Apple Color Emoji","Segoe UI Emoji","Noto Color Emoji",sans-serif;font-size:.85em;line-height:1;vertical-align:.03em;letter-spacing:0;font-style:normal;font-weight:400}.brand-mark{background:transparent}.identity-mark{display:block;width:40px;height:40px;flex-shrink:0}.mobile-identity-mark{display:block;width:28px;height:28px;flex-shrink:0}.feedback h3>.ui-emoji{margin-right:3px}
@media(max-width:850px){.mobile-brand{display:inline-flex;align-items:center;gap:8px}}

.nav-line-icon{display:block;width:20px;height:20px;flex-shrink:0}