:root{
  --navy:#03045e;--blue:#0077b6;--cyan:#00b4d8;--ice:#90e0ef;--pale:#caf0f8;
  --bg:#f7fbfd;--surface:#ffffff;--surface-2:#edf8fc;--text:#10243a;--muted:#5e7183;
  --border:#d6e8ef;--good:#067647;--bad:#b42318;--warn:#b54708;--code:#061829;--code-text:#eaf9ff;
  --shadow:0 12px 34px rgba(3,4,94,.08);--radius:18px
}
html[data-theme="dark"]{
  --bg:#06101d;--surface:#0c1b2a;--surface-2:#102a3d;--text:#e9f5fa;--muted:#a8bfcc;
  --border:#1f4054;--good:#5ad8a1;--bad:#ff938b;--warn:#ffc36b;--code:#020b14;--code-text:#eafaff;
  --shadow:0 12px 34px rgba(0,0,0,.3)
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{margin:0;background:var(--bg);color:var(--text);font-family:Inter,ui-sans-serif,system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;line-height:1.62}
a{color:var(--blue);text-decoration:none} a:hover{text-decoration:underline}
button,input,select{font:inherit}
.wrap{width:min(1160px,calc(100% - 32px));margin:auto}
.skip-link{position:absolute;left:-9999px}.skip-link:focus{left:12px;top:12px;z-index:999;background:#fff;color:#000;padding:10px}
.site-header{position:sticky;top:0;z-index:50;border-bottom:1px solid var(--border);background:color-mix(in srgb,var(--surface) 94%,transparent);backdrop-filter:blur(12px)}
.topbar{min-height:68px;display:flex;align-items:center;justify-content:space-between;gap:16px}
.brand{display:flex;align-items:center;gap:10px;color:var(--text);font-weight:850;letter-spacing:-.025em}
.brand:hover{text-decoration:none}
.brand-mark{width:39px;height:39px;border-radius:12px;background:linear-gradient(135deg,var(--navy),var(--cyan));color:#fff;display:grid;place-items:center;font-size:.72rem;line-height:1.05;box-shadow:var(--shadow)}
.nav{display:flex;gap:4px;align-items:center}.nav a{padding:8px 9px;border-radius:10px;color:var(--text);font-size:.88rem}
.nav a:hover,.nav a[aria-current="page"]{background:var(--surface-2);text-decoration:none}
.icon-btn,.menu-btn{border:1px solid var(--border);background:var(--surface);color:var(--text);padding:8px 10px;border-radius:10px;cursor:pointer}.menu-btn{display:none}
.hero{padding:72px 0 44px;background:radial-gradient(circle at 92% 0%,color-mix(in srgb,var(--cyan) 20%,transparent),transparent 34%)}
.eyebrow{display:inline-block;color:var(--blue);font-weight:850;text-transform:uppercase;letter-spacing:.095em;font-size:.76rem}
.hero h1,.page-hero h1{font-size:clamp(2.15rem,6vw,4.5rem);line-height:1.02;letter-spacing:-.052em;margin:.33em 0 .28em;max-width:980px}
.page-hero h1{font-size:clamp(2rem,5vw,3.55rem)}
.hero p,.page-hero p{font-size:1.07rem;color:var(--muted);max-width:820px}
.page-hero{padding:46px 0 24px}
.breadcrumbs{font-size:.83rem;color:var(--muted);margin-bottom:16px}
.actions{display:flex;flex-wrap:wrap;gap:10px;margin-top:25px}
.btn{display:inline-flex;align-items:center;justify-content:center;border:1px solid transparent;border-radius:12px;background:var(--navy);color:#fff;padding:10px 15px;font-weight:760;cursor:pointer;text-decoration:none}
.btn:hover{background:var(--blue);text-decoration:none}
.btn.secondary{background:var(--surface);border-color:var(--border);color:var(--text)}
.btn.ghost{background:transparent;border-color:var(--border);color:var(--blue)}
.btn.danger{background:transparent;border-color:color-mix(in srgb,var(--bad) 45%,var(--border));color:var(--bad)}
.stats{display:grid;grid-template-columns:repeat(4,1fr);gap:12px;margin-top:34px}
.stat,.card,.concept,.quiz-shell,.notice,.formula-card{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);box-shadow:var(--shadow)}
.stat{padding:18px}.stat strong{display:block;color:var(--navy);font-size:1.45rem}html[data-theme="dark"] .stat strong{color:var(--ice)}
.section{padding:46px 0}.section h2{font-size:clamp(1.55rem,3vw,2.25rem);letter-spacing:-.035em}
.grid{display:grid;grid-template-columns:repeat(3,1fr);gap:16px}
.card{padding:22px}.card h3{margin-top:0}.card p{color:var(--muted)}
.module-link{display:block;color:inherit;transition:.18s ease}.module-link:hover{transform:translateY(-2px);text-decoration:none}
.pill{display:inline-block;background:var(--surface-2);border:1px solid var(--border);padding:4px 9px;border-radius:999px;font-size:.76rem;color:var(--blue);font-weight:800}
.layout{display:grid;grid-template-columns:minmax(0,1fr) 260px;gap:28px;align-items:start}
.toc{position:sticky;top:90px;background:var(--surface);border:1px solid var(--border);border-radius:16px;padding:15px}
.toc strong{display:block;margin-bottom:7px}.toc a{display:block;padding:5px 0;font-size:.84rem;color:var(--muted)}
.module-nav{display:flex;justify-content:space-between;gap:12px;margin:24px 0}.module-nav a{flex:1}
.concept{padding:24px;margin:0 0 20px;scroll-margin-top:90px}.concept h2{margin:.35rem 0 .6rem;font-size:1.55rem;letter-spacing:-.025em}.concept ul{padding-left:20px}
.gotcha{border-left:4px solid var(--warn);background:color-mix(in srgb,var(--warn) 10%,var(--surface));padding:12px 14px;border-radius:10px;margin:16px 0}
.exam-tip{border-left:4px solid var(--cyan);background:var(--surface-2);padding:12px 14px;border-radius:10px;margin:16px 0}
.code-wrap{margin:18px 0}.code-label{font-size:.75rem;font-weight:850;text-transform:uppercase;letter-spacing:.08em;color:var(--cyan);margin-bottom:5px}
.code-block{background:var(--code);color:var(--code-text);border:1px solid #17364c;border-radius:14px;padding:16px;overflow:auto;white-space:pre;font:500 .9rem/1.6 ui-monospace,SFMono-Regular,Menlo,Consolas,monospace}
.formula-explain{color:var(--muted);padding-left:21px}
.inline-quiz{border-top:1px solid var(--border);margin-top:23px;padding-top:18px}
.quiz-head{display:flex;align-items:center;justify-content:space-between;gap:10px;margin-bottom:10px}
.progress{height:8px;background:var(--surface-2);border-radius:999px;overflow:hidden}.progress span{display:block;height:100%;width:0;background:linear-gradient(90deg,var(--blue),var(--cyan))}
.question{padding:17px 0;border-top:1px solid var(--border)}.question:first-of-type{border-top:0}.question-stem{font-weight:760;white-space:pre-line;margin:0 0 12px}
.case-box{background:var(--surface-2);border:1px solid var(--border);border-radius:12px;padding:12px;margin-bottom:12px;color:var(--muted)}
.options{display:grid;gap:8px}.option{display:flex;gap:9px;align-items:flex-start;border:1px solid var(--border);background:var(--surface);border-radius:12px;padding:10px 12px;cursor:pointer}.option:hover{border-color:var(--cyan)}.option input{margin-top:5px}
.feedback{display:none;margin-top:12px;border-radius:12px;padding:13px}.feedback.show{display:block}.feedback.correct{background:color-mix(in srgb,var(--good) 11%,var(--surface));border:1px solid color-mix(in srgb,var(--good) 42%,var(--border))}.feedback.wrong{background:color-mix(in srgb,var(--bad) 9%,var(--surface));border:1px solid color-mix(in srgb,var(--bad) 42%,var(--border))}
.answer-notes{padding-left:20px;color:var(--muted);margin:8px 0 0}.quiz-submit{margin-top:11px}
.yesno-row,.match-row{display:grid;grid-template-columns:1fr 180px;gap:10px;align-items:center;padding:6px 0}
.match-row select,.order-row select,.practice-toolbar select,.practice-toolbar input,.searchbox{padding:9px 10px;border:1px solid var(--border);background:var(--surface);color:var(--text);border-radius:10px}
.order-row{display:grid;grid-template-columns:84px 1fr;gap:10px;align-items:center;padding:5px 0}
.practice-toolbar{display:flex;align-items:center;flex-wrap:wrap;gap:10px;margin:18px 0}.quiz-shell{padding:20px}
.mock-shell{max-width:900px;margin:auto}.mock-top{position:sticky;top:70px;z-index:20;background:var(--surface);border:1px solid var(--border);border-radius:14px;padding:12px 14px;display:flex;justify-content:space-between;align-items:center;gap:12px;margin-bottom:15px;box-shadow:var(--shadow)}
.timer{font-weight:900;font-variant-numeric:tabular-nums}.result-score{font-size:3.2rem;font-weight:900;color:var(--navy)}html[data-theme="dark"] .result-score{color:var(--ice)}
.formula-grid{display:grid;grid-template-columns:repeat(2,1fr);gap:16px}.formula-card{padding:18px}.formula-card h2{margin:.35rem 0}
.searchbox{width:100%;margin:8px 0 20px;padding:12px}
.notice{padding:19px}.small{font-size:.84rem;color:var(--muted)}.muted{color:var(--muted)}
.exam-facts{display:grid;grid-template-columns:repeat(3,1fr);gap:14px}
.footer{border-top:1px solid var(--border);margin-top:48px;padding:34px 0;color:var(--muted);font-size:.88rem}.footer-grid{display:grid;grid-template-columns:2fr 1fr 1fr;gap:20px}.footer a{color:var(--muted)}
.hidden{display:none!important}
@media(max-width:980px){
 .nav{display:none;position:absolute;top:65px;left:16px;right:16px;flex-direction:column;align-items:stretch;background:var(--surface);border:1px solid var(--border);border-radius:14px;padding:10px;box-shadow:var(--shadow)}
 .nav.open{display:flex}.menu-btn{display:inline-block}.layout{grid-template-columns:1fr}.toc{position:relative;top:auto}.grid{grid-template-columns:repeat(2,1fr)}.formula-grid{grid-template-columns:1fr}.exam-facts{grid-template-columns:1fr}.stats{grid-template-columns:repeat(2,1fr)}
}
@media(max-width:640px){
 .wrap{width:min(100% - 20px,1160px)}.brand span:last-child{display:none}.topbar{min-height:62px}.hero{padding-top:46px}.hero h1{font-size:2.4rem}
 .grid,.stats{grid-template-columns:1fr}.concept{padding:18px}.yesno-row,.match-row{grid-template-columns:1fr}.mock-top{top:63px;align-items:flex-start}.footer-grid{grid-template-columns:1fr}.actions .btn{width:100%}.module-nav{flex-direction:column}
}

/* Mobile overflow hardening for lesson, progress and quiz content */
html,body{max-width:100%;overflow-x:hidden}
.layout>*,.layout>div,.concept,.concept-explanation,.inline-quiz,.question,.notice,.quiz-shell,.feedback,.case-box{min-width:0;max-width:100%}
.concept p,.concept li,.concept h2,.concept h3,.question-stem,.option,.answer-notes li,.notice,.feedback{overflow-wrap:anywhere;word-break:normal}
img,svg,video,canvas{max-width:100%;height:auto}
.code-wrap,.code-block,pre{min-width:0;max-width:100%}
.code-block{overflow-x:auto;-webkit-overflow-scrolling:touch}
.concept-table,table{max-width:100%}
.concept-table{display:block;overflow-x:auto;-webkit-overflow-scrolling:touch}
.quiz-head{flex-wrap:wrap;min-width:0}
.quiz-head>*{min-width:0}
.options,.option{min-width:0;max-width:100%}
.option input{flex:0 0 auto}
.yesno-row,.match-row{grid-template-columns:minmax(0,1fr) minmax(0,180px)}
.order-row{grid-template-columns:84px minmax(0,1fr)}
.match-row select,.order-row select,.practice-toolbar select,.practice-toolbar input,.searchbox{min-width:0;max-width:100%}

@media(max-width:640px){
 .layout,.layout>div,.concept,.concept-explanation,.inline-quiz,.question,.notice{width:100%;min-width:0;max-width:100%}
 .concept{overflow:hidden}
 .concept ul,.formula-explain,.answer-notes{padding-left:1.2rem}
 .quiz-head{align-items:flex-start}
 .quiz-head .small{width:100%}
 .yesno-row,.match-row,.order-row{grid-template-columns:1fr}
 .match-row select,.order-row select{width:100%}
 .question-stem{max-width:100%}
 .option{width:100%}
 .code-block{font-size:.82rem;padding:13px}
 .concept-table{width:100%}
}

@media print{
 .site-header,.toc,.inline-quiz,.footer,.actions,.practice-toolbar,.no-print{display:none!important}
 body{background:white;color:black}.wrap{width:100%}.concept,.card,.formula-card{box-shadow:none;border:1px solid #bbb;break-inside:avoid}.page-hero{padding-top:0}
}