:root{color-scheme:dark;--bg:#10131e;--panel:#191e2c;--ink:#edf0fa;--muted:#a1abc0;--line:#30364b;--accent:#b9a5ff;--purple:#8d70ed;--good:#9ce2ba;--bad:#ffb2bb;--gold:#eed4a0;font:16px/1.75 'Segoe UI',Arial,sans-serif}*{box-sizing:border-box}body{margin:0;background:var(--bg);color:var(--ink)}a{color:var(--accent)}button,input,select,textarea{font:inherit}button,a,summary,input,select,textarea{touch-action:manipulation}button,summary{cursor:pointer}button:disabled{opacity:.5;cursor:default}button{color:var(--ink)}button,a,input,textarea,select,summary,math-field{outline-offset:5px}:focus-visible{outline:3px solid #d4bcff}h1,h2,h3,h4{line-height:1.3;margin-top:0;font-weight:720;letter-spacing:-.5px}h1{font-size:clamp(31px,3.7vw,48px);letter-spacing:-1.5px}h2{font-size:25px}h3{font-size:19px}p{margin:0 0 18px}small,.muted{color:var(--muted)}[hidden]{display:none!important}.skip{position:fixed;top:-90px;left:18px;z-index:100;background:var(--panel);padding:12px}.skip:focus{top:10px}.sidebar{position:fixed;inset:0 auto 0 0;width:262px;padding:33px 20px 22px;border-right:1px solid var(--line);background:#151925;display:flex;flex-direction:column;z-index:20}.brand{display:flex;align-items:center;gap:12px;color:var(--ink);text-decoration:none;font-size:15px;font-weight:700;line-height:1.5;padding:0 6px}.brand-icon{width:43px;height:43px;border-radius:13px;display:grid;place-content:center;background:#352b51;color:#cfbfff;font-size:30px;flex-shrink:0}.brand small{display:block;font-size:11px;font-weight:400;color:var(--muted);margin-top:3px}.nav-caption{font-size:9px;letter-spacing:1.6px;color:#8c95ac;margin:49px 12px 17px}.sidebar nav a{display:flex;align-items:center;gap:12px;font-size:13px;color:var(--muted);text-decoration:none;padding:12px 14px;border-radius:9px;margin-bottom:6px}.sidebar nav a>span{width:21px;font-size:20px;color:#969db3}.sidebar nav a.active{background:#342a4e;color:#dccdff;box-shadow:inset 3px 0 #b39af6}.sidebar nav a.active>span{color:#c9b5ff}.sidebar nav a:hover{background:#25283b}.sidebar nav b{font-size:10px;background:#45395f;border-radius:5px;padding:1px 7px;margin-left:auto}.nav-divider{height:1px;background:var(--line);margin:22px 12px}.sidebar-bottom{display:flex;gap:10px;align-items:center;margin-top:auto;padding:20px 12px 0;font-size:11px;color:var(--muted);line-height:1.7}.sidebar-bottom small{display:block;font-size:10px}.status-dot{width:7px;height:7px;border-radius:50%;background:#8dc6a6;flex-shrink:0}.workspace{margin-left:262px}.topbar{height:87px;border-bottom:1px solid #292e40;display:flex;align-items:center;justify-content:space-between;padding:0 46px;gap:20px}.breadcrumb{font-size:10px;color:#a6aec3;letter-spacing:1.2px}.breadcrumb span{margin:0 13px;color:#5f647a}.progress-pill{display:flex;align-items:center;gap:19px;font-size:11px;color:var(--muted);text-decoration:none;white-space:nowrap}.avatar{background:#342d48;color:#cfbfff;border:1px solid #625079;border-radius:50%;height:33px;width:33px;display:grid;place-content:center;font-size:13px;font-weight:700}main{max-width:1220px;margin:0 auto;padding:48px 48px 70px;min-height:calc(100vh - 170px)}.eyebrow{font-size:10px;letter-spacing:2px;color:var(--accent);font-weight:650;margin-bottom:15px}.hero{display:grid;grid-template-columns:minmax(0,1.3fr) minmax(260px,.85fr);gap:58px;align-items:center;margin:8px 0 38px}.hero h1{margin-bottom:20px}.hero h1 em{font-style:normal;color:var(--accent)}.lead{color:var(--muted);font-size:16px;line-height:1.9;max-width:620px}.btn{border:1px solid var(--line);border-radius:9px;padding:11px 19px;background:#252a3d;text-decoration:none;display:inline-flex;align-items:center;justify-content:center;gap:10px;font-size:13px;font-weight:650;line-height:1.7;color:var(--ink)}.btn:hover{filter:brightness(1.15)}.btn.primary{background:var(--purple);border-color:#a58af3;box-shadow:0 4px 0 #4b377f;color:#fff;transform:translateY(-2px)}.btn.primary:active{transform:translateY(1px);box-shadow:0 1px 0 #4b377f}.btn.ghost{background:transparent}.actions{display:flex;gap:12px;flex-wrap:wrap;align-items:center}.hero-demo{position:relative;padding:25px 27px 28px;border:1px solid #45405e;border-radius:19px;background:linear-gradient(140deg,#27233d,#1b2232);box-shadow:0 20px 65px #0002}.demo-top{display:flex;justify-content:space-between;align-items:center;font-size:9px;letter-spacing:1.5px;color:#b2a2cc;margin-bottom:25px}.dot-group{display:flex;gap:5px}.dot-group i{width:5px;height:5px;border-radius:50%;background:#756486}.demo-question{font-size:14px;color:#cbd0e1;line-height:1.7}.hero-formula{font-family:Cambria,'Cambria Math',serif;font-size:30px;text-align:center;padding:20px 0;color:#f0e9ff}.demo-reason{font-size:12px;color:#b0b7cc;border-top:1px solid #494159;padding-top:17px;margin:0}.check-dot{color:var(--good);font-size:15px;margin-right:8px}.stats{display:grid;grid-template-columns:repeat(3,1fr);border:1px solid var(--line);background:#191d2b;border-radius:13px;margin:35px 0 40px;padding:20px 0}.stat{padding:0 26px;border-right:1px solid var(--line)}.stat:last-child{border:0}.stat strong{font-size:23px;display:block;color:#e6dcff;line-height:1.35}.stat small{font-size:11px}.section-title{display:flex;justify-content:space-between;align-items:end;gap:20px;margin-bottom:24px}.section-title h2{margin:0}.section-title p{font-size:12px;color:var(--muted);margin:5px 0 0}.switch{display:flex;gap:4px;background:#202436;padding:4px;border-radius:9px}.switch button{background:none;border:0;border-radius:6px;font-size:11px;padding:7px 11px;color:var(--muted)}.switch button.selected{background:#45365f;color:#e5d6ff}.roadmap{max-width:860px;margin:auto}.chapter{margin:0 0 30px}.chapter-banner{display:grid;grid-template-columns:53px minmax(0,1fr) auto;align-items:center;gap:22px;padding:24px 26px;background:linear-gradient(115deg,#2d2743,#232a3c);border:1px solid #454058;border-radius:15px}.chapter-symbol{height:53px;width:53px;background:#49375980;color:#d7bfff;border:1px solid #b79be83b;border-radius:13px;display:grid;place-content:center;font-size:26px}.chapter-banner h3{margin:0 0 5px;font-size:19px}.chapter-banner p{margin:0;font-size:12px;color:var(--muted)}.chapter-meta{display:flex;gap:14px;align-items:center;font-size:10px;color:#b5b4c9;margin-top:8px}.tag{display:inline-block;border:1px solid #76633f;color:#ead3a9;background:#56462830;padding:2px 7px;border-radius:5px;font-size:9px;letter-spacing:.4px}.chapter progress{width:120px;height:5px;border:0;accent-color:#a087eb;border-radius:5px}progress::-webkit-progress-bar{background:#43435a;border-radius:5px}progress::-webkit-progress-value{background:#ac93f0;border-radius:5px}.chapter details{padding:0 20px}.chapter summary{padding:18px 7px;font-size:12px;color:var(--muted)}.path{display:flex;flex-direction:column;align-items:center;gap:18px;padding:15px 0 28px}.path-node{position:relative;display:flex;align-items:center;gap:22px;width:440px;max-width:90%;padding:10px 0;text-decoration:none;color:var(--ink)}.path-node:nth-child(3n+1){transform:translateX(-23px)}.path-node:nth-child(3n){transform:translateX(23px)}.bubble{position:relative;display:grid;place-items:center;flex-shrink:0;width:65px;height:62px;border-radius:50%;border:2px solid #4a526c;background:#30374b;box-shadow:0 6px 0 #171c2c;color:#c2c8dc;font-size:21px;font-weight:700}.path-node.current .bubble{background:#8d70ed;border-color:#bda4ff;box-shadow:0 6px 0 #503786;outline:3px solid #b8a1ee22;outline-offset:6px;color:white}.path-node.done .bubble{background:#2d604d;border-color:#76a48d;box-shadow:0 6px 0 #193b2f;color:#c0f0d2}.path-node h4{font-size:14px;margin:0 0 5px;letter-spacing:0}.path-node small{font-size:10px}.node-line{position:absolute;left:32px;top:77px;height:20px;border-left:2px dashed #44445c;opacity:.7}.page-heading{max-width:800px;margin-bottom:30px}.page-heading h1{font-size:35px;margin-bottom:12px}.panel{padding:25px 28px;border:1px solid var(--line);border-radius:13px;background:var(--panel);margin-bottom:22px}.panel h2{font-size:21px}.notice{padding:16px 20px;border:1px solid #5e526c;border-left:3px solid var(--accent);border-radius:8px;background:#29233870;font-size:13px;color:#d0c7df;margin:20px 0}.notice.warning{border-color:#7b6440;background:#30281e;color:#ebd5ae}.lesson{max-width:850px;margin:auto}.lesson .goal{font-size:17px;color:#c3b4e1;line-height:1.8}.lesson-body{font-size:16px;line-height:1.95}.lesson-body section{margin:32px 0}.lesson-body h2{font-size:21px;margin-bottom:12px}.worked{background:#222438;border-left:3px solid #a08be2}.worked h3{color:#c9b7fa}.steps{padding-left:23px;margin:12px 0}.steps li{padding:4px 0 8px 8px;font-size:14px}.steps li::marker{color:#baa6f2}.trap{background:#2b2524;border-color:#604e44;font-size:13px}.trap strong{color:var(--gold)}.prerequisites{display:flex;gap:8px;flex-wrap:wrap;font-size:11px;color:var(--muted);margin-top:20px}.prerequisites a{padding:3px 9px;background:#24293a;border-radius:5px;text-decoration:none}.exercise{border:1px solid #41415b;background:#1c2031;border-radius:13px;margin:24px 0;padding:24px}.exercise-head{display:flex;justify-content:space-between;font-size:10px;letter-spacing:1.2px;color:#b8a9d4;margin-bottom:14px}.exercise h3{font-size:17px;font-weight:600;line-height:1.7;letter-spacing:0}.answer-label{display:block;font-size:11px;color:var(--muted);margin:15px 0 7px}.answer-host{min-height:55px}.text-answer,math-field{display:block;width:100%;min-height:55px;background:#121725;border:1px solid #52506e;border-radius:8px;padding:10px 14px;color:var(--ink);font-size:19px;--caret-color:#c4acff;--selection-background-color:#6b52aa77;--contains-highlight-background-color:#6b52aa44;--smart-fence-color:#c4acff;--hue:265}.text-answer{font-family:Cambria,'Cambria Math',Consolas,serif;resize:vertical}.proof-answer{font:14px/1.7 'Segoe UI',sans-serif;min-height:150px}.input-help{font-size:10px;color:var(--muted);margin:7px 0 15px}.choice-list{display:grid;gap:9px;margin:15px 0}.choice{display:flex;gap:10px;align-items:flex-start;border:1px solid var(--line);padding:12px 15px;border-radius:8px;background:#222738;font-size:13px;cursor:pointer}.choice:has(input:checked){border-color:#b099ed;background:#352c4b}.choice input{margin-top:6px;accent-color:#b99bf5}.feedback{margin:17px 0 0;padding:11px 15px;border-radius:7px;font-size:13px}.feedback.correct{background:#21463360;color:#b6eccb;border:1px solid #416c54}.feedback.wrong,.feedback.invalid{background:#512d3760;color:#ffd1d7;border:1px solid #78505c}.feedback.manual{background:#3b324e;color:#dfcffb}.hint,.solution{font-size:13px;line-height:1.8;margin-top:16px;padding:16px 18px;border-radius:8px;background:#29243b;border:1px solid #4e425f}.hint strong,.solution strong{color:#c9b4fc}.rubric{font-size:13px;padding-left:20px}.self-review{display:flex;gap:10px;font-size:13px;align-items:start}.self-review input{margin-top:7px;accent-color:#b79be9}.lesson-nav{display:flex;justify-content:space-between;gap:14px;margin-top:40px;padding-top:25px;border-top:1px solid var(--line)}.filters{display:flex;gap:12px;flex-wrap:wrap;align-items:end;margin-bottom:25px}.field{display:flex;flex-direction:column;gap:6px;font-size:12px;color:var(--muted)}input,select{background:#151a29;color:var(--ink);border:1px solid #454b62;border-radius:7px;padding:9px 11px;max-width:100%}.filter-count{font-size:12px;color:var(--muted);margin-left:auto}.cards{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:18px}.cards>.panel{margin:0}.empty{padding:40px;text-align:center;border:1px dashed #4e4b65;border-radius:13px;color:var(--muted)}.exam-top{display:flex;justify-content:space-between;gap:20px;align-items:center;position:sticky;top:0;background:#181c2bf2;border:1px solid var(--line);padding:15px 22px;border-radius:10px;z-index:10;backdrop-filter:blur(8px)}.timer{font:700 27px/1.3 Consolas,monospace;color:#d8c7ff}.timer.urgent{color:#ffb2bb}.exam-top small{font-size:11px}.exam-note{width:100%;min-height:80px;font-size:13px;background:#121725;color:var(--ink);border:1px solid #41445f;border-radius:7px;padding:10px;resize:vertical}.score{font-size:37px;font-weight:700;color:#c3f0d1}.tool-tabs{display:flex;gap:9px;flex-wrap:wrap;margin-bottom:24px}.tool-tabs .selected{background:#49355f;border-color:#a189cb}.tool-result{padding:18px 22px;background:#121725;border:1px solid #3a3d56;border-radius:9px;margin-top:22px;overflow:auto}.tool-result strong{color:#d4bcff}.table-wrap{overflow:auto}table{border-collapse:collapse;width:100%;font-size:13px}td,th{padding:10px 15px;border-bottom:1px solid var(--line);text-align:left}th{color:#c6b8e3;font-weight:600}.matrix-grid{display:grid;gap:8px;max-width:320px;margin:20px 0}.matrix-grid input{width:100%;text-align:center;padding:8px;min-width:0}.source-link{display:block;text-decoration:none}.source-link h3{font-size:16px;margin-bottom:10px}.source-link p{font-size:12px;color:var(--muted);margin:0}.source-link:hover{border-color:#9a7eca}.symbol{font:25px Cambria,serif;color:#d3c4f0;min-width:70px}.footer{max-width:1220px;margin:0 auto;padding:23px 48px 28px;border-top:1px solid #252b3b;display:flex;justify-content:space-between;gap:20px;font-size:10px;color:#848ea5}.footer a{color:#9e91b8}.toast{position:fixed;bottom:25px;left:50%;transform:translateX(-50%);padding:13px 20px;background:#363047;color:#eee2ff;border:1px solid #79638f;border-radius:9px;z-index:200;font-size:13px;max-width:90vw}.button-link{background:none;border:0;padding:0;color:var(--accent);font-size:12px;text-decoration:underline}.storage-actions{margin-top:28px;padding-top:23px;border-top:1px solid var(--line)}.breadcrumbs{font-size:12px;color:var(--muted);margin-bottom:25px}.breadcrumbs a{text-decoration:none}.reading-time{font-size:11px;color:var(--muted);margin-bottom:10px}.compact{font-size:12px}.formula{font:23px/1.7 Cambria,'Cambria Math',serif;color:#e0d0ff;margin:15px 0}.details-list summary{font-size:15px;color:#d3c2ef;padding:12px 0}.details-list p{color:var(--muted);font-size:13px}math-field::part(virtual-keyboard-toggle){color:#c5b1ed}math-field::part(menu-toggle){display:none}
@media(min-width:1550px){.hero{gap:85px}main{padding-top:62px}.hero-demo{padding:30px 35px}}
@media(max-width:1150px){.sidebar{width:224px;padding-left:13px;padding-right:13px}.workspace{margin-left:224px}main{padding:35px 30px 55px}.topbar{padding:0 30px}.hero{gap:28px;grid-template-columns:1.2fr 1fr}.hero h1{font-size:36px}.chapter-banner{padding:21px;gap:16px}.chapter-banner .btn{font-size:11px;padding:9px 12px}.chapter-banner h3{font-size:18px}.hero-formula{font-size:25px}.breadcrumb{font-size:9px}.footer{padding:20px 30px}.brand{font-size:13px}}
@media(max-width:850px){.sidebar{position:relative;width:100%;height:auto;padding:18px 22px;border-right:0;border-bottom:1px solid var(--line)}.sidebar .brand{font-size:14px}.sidebar nav{display:flex;overflow:auto;gap:7px;margin-top:20px;padding-bottom:4px}.sidebar nav a{font-size:11px;white-space:nowrap;margin:0;padding:8px 12px;gap:6px}.sidebar nav a>span{font-size:16px;width:auto}.sidebar-bottom,.nav-caption,.nav-divider{display:none}.workspace{margin:0}.topbar{height:58px}.hero{gap:30px}main{padding:34px 27px 55px}.hero h1{font-size:37px}.chapter-banner{grid-template-columns:48px 1fr}.chapter-banner>.btn{grid-column:2;justify-self:start}.cards{gap:14px}.footer{font-size:9px}.sidebar nav::-webkit-scrollbar{height:4px}.sidebar nav::-webkit-scrollbar-thumb{background:#5e4c7b;border-radius:8px}}
@media(max-width:600px){main{padding:28px 19px 45px}.topbar{padding:0 19px}.breadcrumb{font-size:8px;letter-spacing:.3px}.breadcrumb span{margin:0 6px}.progress-pill{font-size:9px;gap:9px}.avatar{display:none}.hero{grid-template-columns:1fr;gap:28px;margin:0 0 25px}.hero h1{font-size:38px}.hero-demo{max-width:100%;padding:22px}.lead{font-size:15px}.stats{padding:15px 0;margin:28px 0}.stat{padding:0 13px}.stat strong{font-size:21px}.stat small{font-size:9px}.section-title{align-items:start;flex-direction:column;gap:15px}.section-title h2{font-size:23px}.chapter-banner{padding:19px 17px;gap:15px}.chapter-banner h3{font-size:17px}.chapter-banner p{font-size:11px}.chapter-symbol{height:45px;width:45px;font-size:23px}.chapter details{padding:0 8px}.path-node:nth-child(n){transform:none}.path-node{max-width:95%;gap:18px}.path-node:nth-child(even){padding-left:15px}.bubble{height:55px;width:57px;font-size:18px}.path-node h4{font-size:13px}.node-line{left:27px;top:69px}.panel{padding:20px 19px}.exercise{padding:20px 17px}.exercise h3{font-size:16px}.exercise .actions{gap:8px}.exercise .btn{padding:9px 12px;font-size:11px}.cards{grid-template-columns:1fr}.page-heading h1{font-size:30px}.lesson-body{font-size:15px}.lesson-nav{flex-wrap:wrap}.footer{padding:18px 20px;flex-direction:column;gap:8px}.exam-top{padding:13px 14px;gap:12px}.timer{font-size:22px}.exam-top .btn{font-size:11px;padding:9px}.table-wrap table{min-width:380px}.chapter-meta{gap:9px;flex-wrap:wrap}.lesson-body h2{font-size:20px}}
@media(prefers-reduced-motion:reduce){*{scroll-behavior:auto!important;transition:none!important}}
/* Learning path. */
body{background:radial-gradient(ellipse at 50% 0,#24213c55,transparent 650px),var(--bg)}
.chapter-banner{grid-template-columns:64px minmax(0,1fr) auto;padding:28px;border-radius:20px;gap:24px}
.chapter-symbol{width:64px;height:64px;border-radius:18px;font-size:28px}
.chapter-banner h3{font-size:23px}.chapter-banner p{font-size:14px}.chapter-meta{font-size:12px}
.chapter summary{font-size:14px;padding:20px 8px}.path{gap:28px}.path-node{width:520px;max-width:calc(100% - 80px);min-height:108px;gap:26px}
.bubble{width:84px;height:80px;font-size:28px;border-width:3px}.path-node h4{font-size:17px;line-height:1.5}.path-node small{font-size:12px}.node-line{left:42px;top:98px;height:34px}
.course-shortcuts{display:flex;flex-wrap:wrap;gap:12px;margin:0 auto 30px;max-width:860px}
.exercise-stage{margin:42px 0 12px;border-top:1px solid var(--line);padding-top:22px}.exercise-stage h3{font-size:21px;margin:0 0 7px}.exercise-stage p{color:var(--muted);font-size:13px}
.exercise-number{font-size:11px;color:var(--muted);margin:28px 0 -16px}
.editor-controls{display:flex;flex-wrap:wrap;align-items:center;justify-content:space-between;gap:10px;margin:8px 0}
.editor-modes{display:flex;gap:4px}.editor-modes button,.math-toolbar button{border:1px solid var(--line);border-radius:6px;background:#252a3d;padding:5px 10px;font-size:12px;line-height:1.7;min-height:34px}
.editor-modes [aria-pressed="true"]{background:#45365f;border-color:#a087eb}.editor-state{font-size:10px;color:var(--muted)}
.math-toolbar{display:flex;flex-wrap:wrap;gap:7px;margin:9px 0}.math-toolbar button{min-width:40px}.math-toolbar button:hover{border-color:var(--accent)}
math-field{font-size:22px;overflow-x:auto;max-width:100%;--keycap-background:#282e42;--keycap-text:#edf0fa}
@media(max-width:850px){.chapter-banner{grid-template-columns:56px minmax(0,1fr);gap:18px}.chapter-symbol{height:56px;width:56px}.chapter-banner>.btn{grid-column:2}.sidebar nav{flex-wrap:wrap;overflow:visible}}
@media(max-width:600px){.chapter-banner{padding:20px 17px;gap:14px}.chapter-banner h3{font-size:18px}.chapter-banner p{font-size:12px}.chapter-symbol{height:45px;width:45px}.path-node:nth-child(n){transform:none;max-width:100%;width:100%;padding-left:0;gap:18px}.bubble{height:60px;width:62px;font-size:22px}.path-node h4{font-size:14px}.path-node small{font-size:11px}.node-line{left:31px;top:88px;height:40px}.editor-state{width:100%}.sidebar nav a{font-size:12px}.hero h1{font-size:36px}}