/* Vizekit: the graded exam sheet. Paper, ink, red pen. */
:root {
  --paper: oklch(0.975 0.008 85);
  --paper2: oklch(0.95 0.012 85);
  --grid: oklch(0.86 0.03 240 / 0.45);
  --ink: oklch(0.23 0.015 260);
  --ink2: oklch(0.47 0.015 260);
  --rule: oklch(0.85 0.01 85);
  --pen: oklch(0.55 0.2 27);
  --pen-soft: oklch(0.55 0.2 27 / 0.1);
  --hl: oklch(0.93 0.14 100 / 0.75);
  --ok: oklch(0.55 0.13 150);
  --sans: "Schibsted Grotesk", system-ui, sans-serif;
  --tex: "KaTeX_Main", "Latin Modern Roman", "Times New Roman", serif;
  --hand: "Caveat", "Bradley Hand", cursive;
  --max: 1040px;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --paper: oklch(0.2 0.01 260); --paper2: oklch(0.24 0.012 260); --grid: oklch(0.36 0.03 240 / 0.35);
    --ink: oklch(0.94 0.01 85); --ink2: oklch(0.72 0.015 85); --rule: oklch(0.33 0.01 260);
    --pen: oklch(0.7 0.17 27); --pen-soft: oklch(0.7 0.17 27 / 0.14); --hl: oklch(0.55 0.12 100 / 0.45); --ok: oklch(0.72 0.13 150);
  }
}
:root[data-theme="dark"] {
  --paper: oklch(0.2 0.01 260); --paper2: oklch(0.24 0.012 260); --grid: oklch(0.36 0.03 240 / 0.35);
  --ink: oklch(0.94 0.01 85); --ink2: oklch(0.72 0.015 85); --rule: oklch(0.33 0.01 260);
  --pen: oklch(0.7 0.17 27); --pen-soft: oklch(0.7 0.17 27 / 0.14); --hl: oklch(0.55 0.12 100 / 0.45); --ok: oklch(0.72 0.13 150);
}
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; overflow-x: clip; }
body { margin: 0; background: var(--paper); color: var(--ink); font: 17px/1.6 var(--sans); overflow-x: clip;
  background-image: linear-gradient(var(--grid) 1px, transparent 1px), linear-gradient(90deg, var(--grid) 1px, transparent 1px);
  background-size: 24px 24px; }
a { color: inherit; }
h1, h2, h3 { margin: 0; line-height: 1.05; letter-spacing: -0.03em; font-weight: 800; }
p { margin: 0 0 1em; }
.muted { color: var(--ink2); }
.hl { background: linear-gradient(transparent 55%, var(--hl) 55%, var(--hl) 92%, transparent 92%); padding: 0 .1em; }
.wrap { max-width: var(--max); margin: 0 auto; padding: 0 16px; }

.top { position: sticky; top: 0; z-index: 10; background: color-mix(in oklch, var(--paper) 94%, transparent); border-bottom: 1px solid var(--rule); }
.top .wrap { display: flex; align-items: center; justify-content: space-between; gap: 12px; height: 56px; }
.brand { font-weight: 800; font-size: 21px; letter-spacing: -0.04em; text-decoration: none; }
.brand b { color: var(--pen); }
.topnav { display: flex; align-items: center; gap: 2px; }
.topnav a, .topnav button { white-space: nowrap; font: 600 15px var(--sans); color: var(--ink2); text-decoration: none; padding: 8px 9px; border-radius: 8px; background: none; border: 0; cursor: pointer; }
.topnav a.on { color: var(--ink); text-decoration: underline; text-decoration-color: var(--pen); text-decoration-thickness: 2px; text-underline-offset: 6px; }
main { padding-bottom: 120px; }

.btn { display: inline-flex; align-items: center; justify-content: center; gap: 8px; font: 700 17px var(--sans); text-decoration: none; cursor: pointer;
  padding: 15px 22px; border-radius: 10px; border: 2px solid var(--ink); background: var(--ink); color: var(--paper); transition: transform .12s cubic-bezier(.22,1,.36,1); }
.btn:active { transform: translateY(1px); }
.btn.line { background: transparent; color: var(--ink); }
.btn.pen { background: var(--pen); border-color: var(--pen); color: oklch(0.99 0.005 85); }
.btn.sm { padding: 9px 14px; font-size: 15px; border-width: 1.5px; }
.btn.wide { width: 100%; }
.textbtn { font: 700 17px var(--sans); color: var(--ink); background: none; border: 0; padding: 0; text-decoration: underline; text-decoration-color: var(--pen); text-decoration-thickness: 2px; text-underline-offset: 5px; cursor: pointer; }

.hero { padding: 40px 0 24px; display: grid; gap: 44px; }
@media (min-width: 900px) { .hero { grid-template-columns: 1.05fr 1fr; align-items: center; padding: 72px 0 48px; } }
.kicker { font-family: var(--hand); color: var(--pen); font-size: 27px; font-weight: 600; margin-bottom: 12px; transform: rotate(-1.5deg); display: inline-block; line-height: 1; }
.hero h1 { font-size: clamp(50px, 12vw, 96px); }
.hero .sub { font-size: clamp(21px, 3.4vw, 28px); line-height: 1.28; font-weight: 600; margin: 20px 0 14px; max-width: 22ch; letter-spacing: -0.015em; }
.hero .lead { color: var(--ink2); max-width: 44ch; }
.count { position: relative; display: inline-block; padding: 0 .1em; }
.count svg { position: absolute; left: -12%; top: -14%; width: 124%; height: 128%; overflow: visible; pointer-events: none; }
.count path { fill: none; stroke: var(--pen); stroke-width: 3.2; stroke-linecap: round; stroke-dasharray: 520; stroke-dashoffset: 520; animation: draw 1s .35s cubic-bezier(.22,1,.36,1) forwards; }
@keyframes draw { to { stroke-dashoffset: 0; } }
@media (prefers-reduced-motion: reduce) { .count path { animation: none; stroke-dashoffset: 0; } }
.ctas { display: flex; flex-wrap: wrap; gap: 14px 22px; align-items: center; margin-top: 28px; }

.sheet-paper { position: relative; background: var(--paper); border: 1px solid var(--rule); border-radius: 3px; padding: 26px 20px 46px;
  box-shadow: 0 1px 0 var(--rule), 0 22px 44px -26px oklch(0.2 0.02 260 / 0.4); transform: rotate(0.7deg); }
.sheet-head { display: flex; justify-content: space-between; gap: 10px; font: 15px var(--tex); color: var(--ink2); border-bottom: 1px solid var(--ink); padding-bottom: 6px; margin-bottom: 14px; }
.tex { font-family: var(--tex); font-size: 17.5px; line-height: 1.55; }
.tex p { margin: 0 0 .65em; }
.pts { font-weight: 700; margin-right: .3em; }
.mnote { position: absolute; font: 600 23px var(--hand); color: var(--pen); line-height: 1; }
.mnote.a { top: -15px; right: 14px; background: var(--paper); padding: 0 6px; transform: rotate(-3deg); }
.mnote.b { bottom: 12px; left: 20px; transform: rotate(-2deg); }
.circ { border: 2px solid var(--pen); border-radius: 50%; padding: 0 8px; }

.block { padding: 60px 0; border-top: 1px solid var(--rule); }
.block h2 { font-size: clamp(32px, 6vw, 50px); margin-bottom: 12px; max-width: 18ch; }
.intro { color: var(--ink2); max-width: 56ch; font-size: 18px; }

.xr-tabs { display: flex; gap: 22px; margin: 20px 0 6px; }
.xr-tabs button { font: 700 17px var(--sans); background: none; border: 0; padding: 6px 0; color: var(--ink2); cursor: pointer; border-bottom: 2.5px solid transparent; }
.xr-tabs button.on { color: var(--ink); border-color: var(--pen); }
.xr { list-style: none; margin: 0; padding: 0; max-width: 760px; }
.xr li { display: grid; grid-template-columns: 1fr auto; gap: 2px 16px; align-items: center; padding: 15px 0; border-bottom: 1px dashed var(--rule); }
.xr .t { font-weight: 600; }
.xr .boxes { display: flex; gap: 5px; }
.xr .boxes i { width: 19px; height: 19px; border: 1.5px solid var(--ink2); border-radius: 3px; display: block; }
.xr .boxes i.on { background: var(--pen); border-color: var(--pen); }
.xr .pct { font-size: 14px; color: var(--ink2); }
.xr li.zero .t { color: var(--ink2); text-decoration: line-through; text-decoration-color: var(--pen); text-decoration-thickness: 2px; }
.xr-note { font: 600 25px var(--hand); color: var(--pen); margin: 16px 0 0; transform: rotate(-1deg); }
.src { font-size: 14px; color: var(--ink2); margin-top: 14px; max-width: 70ch; }
.fz { margin-top: 30px; max-width: 760px; border: 2px solid var(--pen); border-radius: 6px; padding: 16px 18px; background: var(--pen-soft); }
.fz b { color: var(--pen); }

.cover { width: 100%; max-width: 760px; border-collapse: collapse; font-size: 16px; margin-top: 16px; }
.cover th { text-align: left; font: 600 13px var(--sans); color: var(--ink2); padding: 8px 6px; border-bottom: 2px solid var(--ink); }
.cover th:last-child { text-align: right; }
.cover td { padding: 15px 6px; border-bottom: 1px solid var(--rule); vertical-align: top; }
.cover td:first-child { font: 700 19px var(--tex); width: 46px; }
.cover td small { display: block; color: var(--ink2); font-size: 14px; margin-top: 2px; }
.cover td.n { text-align: right; white-space: nowrap; font-variant-numeric: tabular-nums; font-weight: 700; }
.cover .free { font: 600 21px var(--hand); color: var(--ok); margin-left: 6px; }
.extras { display: grid; gap: 12px; margin: 28px 0 0; max-width: 700px; padding: 0; list-style: none; }
.extras li { padding-left: 32px; position: relative; }
.extras li::before { content: "✓"; position: absolute; left: 4px; top: -4px; font: 600 26px var(--hand); color: var(--pen); }

.price-grid { display: grid; gap: 32px; align-items: start; }
@media (min-width: 860px) { .price-grid { grid-template-columns: 1fr 1fr; } }
.gradebox { border: 2px solid var(--ink); border-radius: 6px; padding: 22px; background: var(--paper); }
.gradebox .lbl { font: 600 13px var(--sans); color: var(--ink2); }
.amount { display: flex; align-items: baseline; gap: 16px; margin: 8px 0 4px; }
.amount .now { font-size: clamp(58px, 12vw, 84px); font-weight: 800; letter-spacing: -0.05em; line-height: 1; }
.amount .was { position: relative; font-size: 24px; color: var(--ink2); }
.amount .was::after { content: ""; position: absolute; left: -4px; right: -4px; top: 52%; height: 3px; background: var(--pen); transform: rotate(-9deg); border-radius: 2px; }
.seg { display: flex; border: 1.5px solid var(--ink); border-radius: 10px; overflow: hidden; margin: 18px 0 12px; }
.seg button { flex: 1; font: 700 16px var(--sans); padding: 11px; border: 0; background: transparent; color: var(--ink); cursor: pointer; }
.seg button.on { background: var(--ink); color: var(--paper); }
input, textarea { width: 100%; font: 17px var(--sans); color: var(--ink); background: var(--paper); border: 1.5px solid var(--ink2); border-radius: 10px; padding: 14px; margin: 0 0 10px; }
input:focus, textarea:focus { outline: 2px solid var(--pen); outline-offset: 1px; border-color: transparent; }
.err { color: var(--pen); font-size: 15px; margin: 6px 0 0; }
.done-msg { font: 600 30px var(--hand); color: var(--pen); line-height: 1.1; margin: 8px 0; }
.fine { font-size: 14px; color: var(--ink2); margin: 12px 0 0; }

.story p { max-width: 58ch; font-size: 18px; }
.sign { font: 600 38px var(--hand); color: var(--pen); line-height: 1; }
.faq details { border-bottom: 1px solid var(--rule); padding: 17px 0; max-width: 760px; }
.faq summary { cursor: pointer; font-weight: 700; list-style: none; display: flex; justify-content: space-between; gap: 12px; }
.faq summary::-webkit-details-marker { display: none; }
.faq summary::after { content: "+"; font: 600 28px var(--hand); color: var(--pen); line-height: .8; }
.faq details[open] summary::after { content: "–"; }
.faq details p { color: var(--ink2); margin: 10px 0 0; max-width: 62ch; }
.foot { padding: 40px 16px; text-align: center; font-size: 14px; color: var(--ink2); }

.chead { padding: 36px 0 8px; }
.chead h1 { font-size: clamp(40px, 9vw, 66px); }
.chead .scope { color: var(--ink2); margin-top: 12px; max-width: 60ch; }
.okline { font: 600 27px var(--hand); color: var(--ok); margin-top: 12px; }
.upsell { margin-top: 20px; display: flex; flex-wrap: wrap; align-items: center; gap: 12px 18px; padding: 14px 16px; border: 1.5px dashed var(--pen); border-radius: 8px; max-width: 760px; }
.upsell.big { display: block; padding: 28px 20px; margin: 44px 0; }
.upsell.big h2 { font-size: 30px; margin-bottom: 8px; }
.sec { font-size: 32px; margin: 48px 0 16px; }
.units { border-top: 2px solid var(--ink); max-width: 760px; }
.unit { display: grid; grid-template-columns: 44px 1fr; gap: 6px 14px; padding: 18px 4px; border-bottom: 1px solid var(--rule); text-decoration: none; }
.unit .k { font: 700 26px var(--tex); }
.unit h3 { font-size: 21px; letter-spacing: -0.02em; margin-bottom: 4px; }
.unit p { margin: 0; font-size: 15px; color: var(--ink2); }
a.unit:hover h3 { text-decoration: underline; text-decoration-color: var(--pen); text-underline-offset: 4px; }
.unit.locked { color: var(--ink2); }
.unit .free { font: 600 22px var(--hand); color: var(--ok); margin-left: 6px; }
.bar { height: 3px; background: var(--rule); margin-top: 10px; max-width: 320px; }
.bar i { display: block; height: 100%; background: var(--ok); }
.plan ol { padding-left: 22px; max-width: 70ch; } .plan li { margin: 8px 0; }
.exlinks { display: flex; flex-wrap: wrap; gap: 8px 18px; margin-top: 10px; }
.exlinks a { font-weight: 600; text-decoration-color: var(--pen); text-underline-offset: 3px; }
.back { display: inline-block; margin-top: 22px; color: var(--ink2); text-decoration: none; font-weight: 700; }
.note { background: var(--paper2); padding: 14px 16px; border-radius: 8px; margin-top: 18px; max-width: 70ch; }
.note p { margin: 0; }
.toc { position: sticky; top: 56px; z-index: 5; display: flex; gap: 20px; overflow-x: auto; padding: 13px 0; background: var(--paper); border-bottom: 1px solid var(--rule); scrollbar-width: none; margin-top: 22px; }
.toc a { flex: none; text-decoration: none; font-weight: 700; color: var(--ink2); font-size: 15px; }
.toc a:hover { color: var(--ink); }
.lesson { margin: 36px 0; max-width: 70ch; }
.lesson h2 { font-size: 26px; margin-bottom: 12px; }
.panel { margin: 32px 0; padding: 20px; border: 1.5px solid var(--ink); border-radius: 6px; background: var(--paper); max-width: 760px; }
.panel h2 { font-size: 25px; margin-bottom: 10px; }
.panel.trap { border-color: var(--pen); }
.panel.trap h2 { color: var(--pen); }
.trap li { margin: 10px 0; }
.formulas { display: grid; gap: 2px 18px; margin: 0; }
@media (min-width: 700px) { .formulas { grid-template-columns: 1fr 1fr; } }
.formulas dt { font-size: 14px; color: var(--ink2); margin-top: 10px; }
.formulas dd { margin: 0; overflow-x: auto; }
.prob { position: relative; background: var(--paper); border: 1px solid var(--rule); border-top: 2px solid var(--ink); padding: 18px 18px 14px; margin: 20px 0; max-width: 760px; }
.prob.done { border-top-color: var(--ok); }
.ph { display: flex; justify-content: space-between; gap: 10px; font: 700 16px var(--tex); margin-bottom: 8px; }
.lv { color: var(--ink2); font: 600 13px var(--sans); letter-spacing: 1px; }
.prob .q { font-family: var(--tex); font-size: 18px; line-height: 1.55; }
.prob details { margin-top: 14px; border-top: 1px dashed var(--rule); padding-top: 10px; }
.prob summary { cursor: pointer; font-weight: 700; color: var(--pen); }
.prob details.inner summary { color: var(--ink2); }
.ans { background: var(--pen-soft); border-radius: 6px; padding: 10px 14px; margin: 10px 0; }
.ans p { margin: 4px 0; }
.row { display: flex; gap: 10px; flex-wrap: wrap; margin-top: 12px; }
.fig { margin: 14px 0; text-align: center; color: var(--ink); }
.fig svg { max-width: 100%; height: auto; max-height: 280px; }
.katex-display { overflow-x: auto; overflow-y: hidden; padding: 4px 0; }
.katex .katex-mathml { position: absolute; width: 1px; height: 1px; overflow: hidden; clip-path: inset(50%); }
.lesson, .prob, .panel, .ans { overflow-wrap: anywhere; min-width: 0; }
.lesson .katex, .prob .katex, .panel .katex { white-space: normal; }
pre, code { font-size: 15px; }
.lesson table { display: block; overflow-x: auto; border-collapse: collapse; }
.lesson td, .lesson th { border: 1px solid var(--rule); padding: 6px 10px; }
.loading { padding: 100px 0; text-align: center; font: 600 30px var(--hand); color: var(--pen); }
.fab { position: fixed; right: 16px; bottom: calc(16px + env(safe-area-inset-bottom)); z-index: 20; font: 700 16px var(--sans); padding: 14px 20px; border-radius: 999px;
  background: var(--ink); color: var(--paper); border: 0; cursor: pointer; box-shadow: 0 10px 30px -10px oklch(0.2 0.02 260 / 0.5); }

.sheet { position: fixed; inset: 0; z-index: 50; background: oklch(0.15 0.01 260 / 0.5); display: flex; align-items: flex-end; justify-content: center; }
.sheet[hidden] { display: none; }
.sheet-card { position: relative; width: 100%; max-width: 580px; max-height: 88vh; overflow: auto; background: var(--paper); border-top: 2px solid var(--ink);
  border-radius: 14px 14px 0 0; padding: 26px 18px calc(18px + env(safe-area-inset-bottom)); }
@media (min-width: 700px) { .sheet { align-items: center; } .sheet-card { border-radius: 10px; border: 2px solid var(--ink); } }
.sheet-card h3 { font-size: 26px; margin-bottom: 14px; }
.x { position: absolute; top: 8px; right: 12px; background: none; border: 0; color: var(--ink2); font-size: 30px; cursor: pointer; }
.chat { max-height: 52vh; overflow: auto; display: grid; gap: 10px; margin-bottom: 10px; }
.msg { padding: 10px 14px; border-radius: 10px; background: var(--paper2); }
.msg.user { background: transparent; border: 1.5px solid var(--rule); justify-self: end; max-width: 90%; }
.msg p { margin: 4px 0; }
.pending { font: 600 22px var(--hand); color: var(--pen); }
.katex-display > .katex { white-space: nowrap !important; }

/* demo layer: sims + stepper */
.sim { margin: 34px 0; padding: 18px 16px; border: 2px solid var(--ink); border-radius: 6px; background: var(--paper); max-width: 760px; }
.sim-head { font-size: 17px; margin-bottom: 8px; }
.sim-svg { width: 100%; height: auto; display: block; }
.sim-svg.small { margin-top: 6px; border-top: 1px dashed var(--rule); padding-top: 6px; }
.sim-ctl { display: grid; gap: 6px; margin: 8px 0; }
.sim-ctl label { display: grid; grid-template-columns: 44px 1fr 64px; align-items: center; gap: 10px; font: 700 17px var(--tex); }
.sim-ctl input[type=range] { margin: 0; padding: 0; border: 0; accent-color: var(--pen); height: 28px; background: none; }
.sim-ctl output { font: 600 15px var(--sans); text-align: right; font-variant-numeric: tabular-nums; }
.sim-read { font-size: 17px; min-height: 30px; }
.sim-note { color: var(--ink2); margin: 8px 0 0; }
.sim-note .hand, .stepper .hand { font: 600 24px var(--hand); color: var(--pen); }
.sim svg .ink { stroke: var(--ink); stroke-width: 2; }
.sim svg .wall { fill: var(--ink2); opacity: .35; }
.sim svg .path { fill: none; stroke: var(--pen); stroke-width: 2.4; stroke-dasharray: 5 4; }
.sim svg .ball { fill: var(--pen); }
.sim svg .max { stroke: var(--pen); stroke-width: 2; }
.sim svg .arc { fill: none; stroke: var(--ink2); stroke-width: 1.5; }
.sim svg .lbl { font: 12px var(--sans); fill: var(--ink2); }
.sim svg .handt { font: 600 17px var(--hand); fill: var(--pen); }
.sim svg .faint { stroke: var(--rule); stroke-width: 1.5; }
.sim svg .ink2 { fill: none; stroke: var(--ink); stroke-width: 2.2; }
.sim svg .ring { fill: none; stroke: var(--pen); stroke-width: 2.2; }
.sim svg .charged { fill: var(--pen-soft); stroke: var(--pen); stroke-width: 1.5; }
.sim svg .plus { font: 700 10px var(--sans); fill: var(--pen); }
.sim svg .gs { fill: none; stroke: var(--ink); stroke-width: 2; stroke-dasharray: 6 5; }
.sim svg .evec { stroke: var(--ink2); stroke-width: 1.6; }
.stepper { margin-top: 14px; border-top: 1px dashed var(--rule); padding-top: 12px; }
.st-top { display: flex; justify-content: space-between; font-weight: 700; color: var(--pen); }
.st-score { font: 600 22px var(--hand); }
.st-list { list-style: none; padding: 0; margin: 10px 0; display: grid; gap: 10px; }
.st-list li { position: relative; padding: 8px 12px 8px 54px; background: var(--paper2); border-radius: 6px; animation: stin .35s cubic-bezier(.22,1,.36,1); overflow-wrap: anywhere; }
.st-list li p { margin: 4px 0; }
.st-pts { position: absolute; left: 10px; top: 8px; font: 600 22px var(--hand); color: var(--pen); }
@keyframes stin { from { opacity: 0; transform: translateY(6px); } }
@media (prefers-reduced-motion: reduce) { .st-list li { animation: none; } }
.st-rubric { margin-top: 12px; border: 1.5px solid var(--pen); border-radius: 6px; padding: 10px 14px; }
.st-rubric ul { margin: 6px 0 0; padding-left: 18px; }
.sim-ctl input[type=range]:focus { outline: none; }
.sim-ctl input[type=range]:focus-visible { outline: 2px solid var(--pen); outline-offset: 2px; }
.sim svg .ladder { stroke: var(--ink); stroke-width: 4; stroke-linecap: round; }
.sim svg .arrow { stroke: var(--ink2); stroke-width: 2; marker-end: none; }
.mk-clock { position: sticky; top: 64px; z-index: 6; display: inline-block; margin: 12px 0; padding: 6px 14px; border: 2px solid var(--pen); border-radius: 999px; background: var(--paper); font: 700 22px var(--sans); font-variant-numeric: tabular-nums; color: var(--pen); }
.mk-score { display: flex; align-items: center; gap: 8px; margin-top: 12px; font-weight: 700; }
.mk-score input { width: 80px; margin: 0; padding: 8px 10px; }
.mk-result { margin-top: 24px; max-width: 760px; }