:root {
  --bg: #080a11;
  --surface: #11141e;
  --surface-2: #1a1e2c;
  --diagram: #0c0f19;
  --line: rgba(255, 255, 255, .09);
  --text: #f2f4fb;
  --text-2: #c8cde2;
  --muted: #8f97b5;

  --blue: #3b6bff;
  --blue-d: #2447d6;
  --blue-l: #7fa6ff;
  --deep: #0f1d4d;          /* deep purple surface */
  --navy: #0a1230;          /* dark blue, used sparingly */
  --hl: #d6e2ff;
  --coral: #ff6b5e;
  --mint: #2fd5a6;
  --on-light: #14122b;

  --soft: 0 12px 32px rgba(0, 0, 0, .45);
  --lift: 0 28px 70px rgba(0, 0, 0, .6);
  --display: "Plus Jakarta Sans", system-ui, sans-serif;
  --sans: "Figtree", system-ui, sans-serif;
  --mono: "JetBrains Mono", ui-monospace, monospace;
  --r: 0px;                 /* corner radius for the whole site; set e.g. 10px to soften */
  color-scheme: dark;
}

* { box-sizing: border-box; }
[hidden] { display: none !important; }
html { scroll-behavior: smooth; scroll-padding-top: 76px; }
body { margin: 0; background: var(--bg); color: var(--text); font: 400 1.0625rem/1.6 var(--sans); -webkit-font-smoothing: antialiased; }
img { max-width: 100%; }
img[src$=".svg"], img[src$=".gif"] { image-rendering: pixelated; }
img[src$="logo-mark.svg"] { image-rendering: auto; }
h1, h2, h3, h4 { font-family: var(--display); line-height: 1.05; margin: 0; font-weight: 800; letter-spacing: -.025em; }
a { color: inherit; }
button { font-family: inherit; }
.wrap { width: min(1180px, 100% - 32px); margin-inline: auto; }
.narrow { max-width: 760px; }
.center { text-align: center; }
.micro { font-size: .85rem; color: var(--muted); margin: 8px 0 0; }
:focus-visible { outline: 3px solid var(--hl); outline-offset: 2px; }

.eyebrow { font: 700 .78rem var(--mono); text-transform: uppercase; letter-spacing: .1em; color: var(--blue-l); margin: 0 0 14px; }
.hero .eyebrow, .sun .eyebrow, .final .eyebrow { color: var(--blue-l); }
h2 { font-size: clamp(2.1rem, 4.6vw, 3.2rem); max-width: 26ch; }
.sub { color: var(--muted); max-width: 72ch; margin: 14px 0 28px; font-size: 1.1rem; }
.sun .sub { color: var(--text-2); }

/* BUTTONS */
.btn { display: inline-block; font: 700 1rem var(--sans); cursor: pointer; text-decoration: none; text-align: center; padding: 14px 26px; border: 0; border-radius: var(--r); transition: transform .15s, box-shadow .15s, background .15s; }
.btn:hover { transform: translateY(-2px); }
.btn.sm { padding: 9px 18px; font-size: .92rem; }
.btn.big { padding: 18px 36px; font-size: 1.15rem; }
.btn.wide { width: 100%; }
.btn.primary { background: var(--blue); color: #fff; box-shadow: none; }
.btn.primary:hover { background: #5f87ff; }
.btn.ink { background: #fff; color: var(--on-light); }
.btn.hi { background: #fff; color: var(--on-light); }
.btn.ghost-d { background: var(--surface-2); color: var(--text); }
.btn.ghost-l { background: transparent; color: #fff; box-shadow: inset 0 0 0 2px rgba(255, 255, 255, .3); }

/* NAV */
.nav { position: sticky; top: 0; z-index: 30; display: flex; align-items: center; gap: 24px; padding: 10px max(16px, calc((100% - 1180px) / 2)); background: rgba(11, 11, 15, .88); backdrop-filter: blur(12px); border-bottom: 1px solid var(--line); }
.logo { display: flex; align-items: center; gap: 10px; text-decoration: none; font: 800 1.35rem var(--display); letter-spacing: -.03em; }
.logo i { font-style: normal; color: var(--blue-l); }
.nav nav { display: flex; gap: 26px; margin-left: auto; }
.nav nav a { text-decoration: none; font-weight: 600; font-size: .95rem; color: var(--text-2); }
.nav nav a:hover { color: #fff; }
.nav-right { display: flex; align-items: center; gap: 12px; }
.meter { font: 600 .82rem var(--mono); background: var(--surface-2); color: var(--text); border: 0; border-radius: var(--r); padding: 6px 12px; cursor: pointer; }
.meter b { color: var(--blue-l); }

/* HERO */
.hero { position: relative; overflow: hidden; padding: 64px 0 88px; background: linear-gradient(180deg, #0c1a47 0%, var(--bg) 78%); isolation: isolate; }
.hero::before { content: ""; position: absolute; inset: 0; z-index: -1; background: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='56' height='100'%3E%3Cpath d='M28 0L56 16V50L28 66L0 50V16Z M28 66V100' fill='none' stroke='%237fa6ff' stroke-opacity='.11' stroke-width='1.5'/%3E%3C/svg%3E"); -webkit-mask-image: linear-gradient(180deg, #000 0%, transparent 85%); mask-image: linear-gradient(180deg, #000 0%, transparent 85%); }
.hero-top { display: grid; grid-template-columns: 1fr 1.05fr; gap: 48px; align-items: start; margin-bottom: 28px; }
.hero h1 { font-size: clamp(2.6rem, 5vw, 4.3rem); margin-bottom: 22px; }
.hero-copy { padding-top: 24px; position: sticky; top: 90px; }
.marked { color: var(--blue-l); background: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 120 12' preserveAspectRatio='none'%3E%3Cpath d='M2 8 Q 15 1 30 7 T 60 7 T 90 7 T 118 6' fill='none' stroke='%23ffffff' stroke-width='3.5' stroke-linecap='round'/%3E%3C/svg%3E") 0 100% / 100% 14px no-repeat; padding-bottom: 10px; }
.lead { font-size: 1.2rem; max-width: 50ch; color: var(--text-2); margin: 0 0 28px; }

.picker { display: flex; flex-wrap: wrap; gap: 12px; align-items: flex-end; background: var(--surface); border: 1px solid var(--line); border-radius: var(--r); padding: 14px; box-shadow: var(--lift); max-width: 560px; }
.picker label { display: grid; gap: 4px; font: 700 .7rem var(--mono); text-transform: uppercase; letter-spacing: .08em; color: var(--muted); flex: 1 1 130px; }
.picker select { font: 600 1rem var(--sans); color: var(--text); background: var(--surface-2); border: 1px solid var(--line); border-radius: var(--r); padding: 12px 10px; }
.picker .btn { flex: 0 0 auto; padding: 13px 26px; }

.points { list-style: none; margin: 36px 0 0; padding: 28px 0 0; border-top: 1px solid var(--line); display: grid; gap: 14px; max-width: 520px; }
.points li { position: relative; padding-left: 34px; color: var(--text-2); }
.points li::before { content: ""; position: absolute; left: 0; top: 2px; width: 20px; height: 23px; background: var(--blue); clip-path: polygon(50% 0, 100% 25%, 100% 75%, 50% 100%, 0 75%, 0 25%); }
.points li::after { content: ""; position: absolute; left: 7px; top: 11px; width: 6px; height: 6px; border-radius: 50%; background: #fff; }
.points b { color: #fff; }

/* SHOWCASE (hero right) */
.showcase { display: grid; gap: 16px; }
.sc-strip { margin-bottom: 56px; }
.sc-row { display: grid; grid-template-columns: 1fr 2.2fr; gap: 16px; }
.sc-tutors, .sc-labs { position: relative; overflow: hidden; border-radius: var(--r); text-decoration: none; color: var(--text); min-height: 132px; box-shadow: var(--lift); transition: transform .15s; }
.sc-tutors:hover, .sc-labs:hover { transform: translateY(-3px); }
.sc-tutors { background: var(--surface); border: 1px solid var(--line); }
.reel { position: absolute; inset: 0; display: flex; align-items: center; gap: 14px; width: max-content; padding-left: 34%; animation: reel 46s linear infinite; }
.reel span { flex: 0 0 auto; width: 78px; height: 90px; clip-path: polygon(50% 0, 100% 25%, 100% 75%, 50% 100%, 0 75%, 0 25%); display: grid; place-items: center; background: var(--c); }
.reel img { height: 44px; width: auto; }
@keyframes reel { to { transform: translateX(-50%); } }
.sc-text { display: grid; gap: 2px; }
.sc-tutors .sc-text { position: absolute; inset: 0 auto 0 0; width: 32%; min-width: 230px; z-index: 1; padding: 20px; align-content: center; background: linear-gradient(90deg, var(--surface) 72%, transparent); }
.sc-text b { font: 800 1.2rem/1.1 var(--display); letter-spacing: -.02em; }
.sc-text span { font-size: .85rem; color: var(--muted); }
.sc-labs { background: var(--deep); border: 1px solid rgba(127, 166, 255, .3); display: flex; align-items: center; gap: 16px; padding: 18px 22px; }
.sc-labs svg { width: 46px; height: 52px; flex: 0 0 auto; background: rgba(127, 166, 255, .22); clip-path: polygon(50% 0, 100% 25%, 100% 75%, 50% 100%, 0 75%, 0 25%); padding: 12px 11px; }

.sc-diff { background: var(--surface); border: 1px solid var(--line); border-radius: var(--r); padding: 22px; box-shadow: var(--lift); }
.sc-diff header { margin-bottom: 12px; }
.pill { display: inline-block; font: 700 .7rem var(--mono); text-transform: uppercase; letter-spacing: .06em; background: rgba(59, 107, 255, .18); color: var(--blue-l); padding: 4px 10px; border-radius: var(--r); }
.sc-diff h3 { font-size: 1.6rem; margin: 10px 0 2px; }
.sc-diff header p { margin: 0; color: var(--muted); font-size: .95rem; }
.dg-grid { stroke: rgba(255, 255, 255, .07); stroke-width: 1; }
.dg-axis { stroke: rgba(255, 255, 255, .28); stroke-width: 1.5; }
.dg-tick { fill: #7a82a3; font: 500 11px var(--mono); }
.dg-name { fill: var(--text-2); font: 700 12px var(--mono); }
.dg-curve { fill: none; stroke: var(--blue-l); stroke-width: 3.5; stroke-linecap: round; stroke-linejoin: round; }
.dg-grad { fill: none; stroke: var(--mint); stroke-width: 3.5; stroke-linecap: round; }
.dg-tan { stroke: var(--coral); stroke-width: 3; stroke-linecap: round; }
.dg-guide { stroke: rgba(255, 255, 255, .3); stroke-width: 1.5; stroke-dasharray: 4 5; }
.dg-pt { fill: #fff; stroke: var(--blue); stroke-width: 4; }
.dg-pt2 { fill: var(--mint); stroke: var(--diagram); stroke-width: 3; }
.dg-ring { fill: none; stroke: var(--mint); stroke-width: 5; opacity: 0; transition: opacity .15s; }
.dg-ring.on { opacity: 1; }
.dg-stat { fill: #7a82a3; opacity: .9; }
.dg-read { display: flex; flex-wrap: wrap; gap: 8px 18px; align-items: baseline; margin: 12px 0 8px; font: 500 .85rem var(--mono); color: var(--muted); }
.dg-read b { color: var(--text); font-weight: 700; margin-left: 3px; }
.dg-read em { margin-left: auto; font: 700 .78rem var(--mono); font-style: normal; background: rgba(59, 107, 255, .18); color: var(--blue-l); padding: 4px 12px; border-radius: var(--r); transition: background .15s, color .15s; }
.dg-read em.zero { background: var(--mint); color: var(--on-light); }

/* SOLVER (tablet) */

.tablet-wrap { position: relative; max-width: 1120px; margin: 0 auto; padding-right: 34px; }
.tablet { position: relative; background: #040509; padding: 16px; border-radius: 22px; border: 2px solid #2a3150; box-shadow: 0 40px 90px rgba(0, 0, 0, .75), inset 0 0 0 1px #10162c; }
.tablet .cam { position: absolute; top: 6px; left: 50%; width: 6px; height: 6px; border-radius: 50%; background: #1b2240; }
.screen { display: grid; grid-template-columns: 1fr 1fr; min-height: 560px; background: #0a0c14; overflow: hidden; border-radius: 6px; position: relative; }
.screen::after { content: ""; position: absolute; top: 0; bottom: 0; left: 50%; width: 10px; translate: -50% 0; background: linear-gradient(90deg, #0a0c14, #2a3150 50%, #0a0c14); }
.pencil { position: absolute; right: 0; top: 56px; bottom: 56px; width: 14px; border-radius: 8px; background: linear-gradient(90deg, #f4f5fa, #b9bdd0); box-shadow: 0 10px 24px rgba(0, 0, 0, .6); rotate: 2deg; }
.pencil::after { content: ""; position: absolute; left: 3px; right: 3px; bottom: -8px; height: 12px; background: #2a3150; clip-path: polygon(0 0, 100% 0, 50% 100%); }

.t-paper { position: relative; padding: 24px 26px 74px; background: #07080d; color: #e8ecf8; font: 400 .88rem/1.55 var(--sans); }
.t-pg { margin: 0 0 14px; text-align: center; font-size: .8rem; color: #8b93b3; }
.t-q { margin: 0 0 12px; } .t-q b { margin-right: 10px; } .t-q em { font-style: normal; font-weight: 700; float: right; margin-left: 10px; }
.t-q mark { background: rgba(59, 107, 255, .5); color: #fff; padding: 1px 3px; }
.t-fig { display: block; width: 100%; max-width: 330px; margin: 6px auto 16px; }
.t-fig .bond path, #mol2d .bond path { stroke: #cfd6ee; stroke-width: 2.2; stroke-linecap: round; fill: none; }
.t-fig .atom text { fill: #eef1fb; font: 600 17px var(--sans); text-anchor: middle; }
.t-lines { display: grid; gap: 22px; margin-top: 26px; }
.t-lines i { display: block; border-bottom: 1px dotted #5a6285; }
.t-tools { position: absolute; left: 18px; right: 18px; bottom: 16px; display: flex; align-items: center; gap: 4px; padding: 8px 12px; background: #141a2e; border: 1px solid #263055; border-radius: var(--r); color: #aab3d4; font-size: .95rem; }
.t-tools span { padding: 2px 7px; }
.t-tools .sep { width: 1px; height: 18px; padding: 0; margin: 0 6px; background: #263055; }
.t-tools .pg { margin-left: auto; font: 700 .72rem var(--mono); background: #0a0e1c; border: 1px solid #263055; }

.t-side { display: flex; flex-direction: column; background: #0c0f1b; min-width: 0; }
.t-head { display: flex; align-items: center; gap: 10px; padding: 12px 14px 12px 22px; background: #1c3aa8; font-size: .95rem; }
.t-head .grow { flex: 1; }
.t-head .qtag { font: 700 .68rem var(--mono); background: rgba(255, 255, 255, .22); padding: 2px 8px; }
.t-btn { display: inline-grid; place-items: center; width: 28px; height: 28px; background: rgba(255, 255, 255, .88); color: #14122b; font-weight: 700; font-size: .8rem; }
.t-side .tabs { padding: 10px 14px 0 22px; }
.t-body { flex: 1; overflow-y: auto; padding: 18px 22px 8px; }
.t-body h4 { font: 800 1.15rem var(--display); margin-bottom: 8px; }
.t-ans { margin: 0 0 12px; color: var(--text-2); } .t-ans b { color: #fff; } .t-ans.small { font-size: .88rem; color: var(--muted); }
.t-ask { display: flex; align-items: center; gap: 10px; margin: 8px 16px 16px 22px; padding: 10px 12px; background: #11162a; border: 1px solid #263055; border-radius: var(--r); color: var(--muted); text-align: left; font: 500 .88rem var(--sans); cursor: pointer; }
.t-ask:hover { border-color: var(--blue); color: var(--text); }
.t-ask span { flex: 1; } .t-ask i { font-style: normal; display: grid; place-items: center; width: 30px; height: 30px; background: var(--blue); color: #fff; }

.mol { background: #070a14; border: 1px solid #1c2442; margin: 4px 0 12px; }
.mol-bar { display: flex; justify-content: center; padding: 10px 0 0; }
#mol2d { display: block; width: 100%; height: auto; max-height: 230px; }
#mol2d .hl { fill: rgba(59, 107, 255, .16); stroke: rgba(127, 166, 255, .8); stroke-width: 2; stroke-dasharray: 5 4; }
#mol2d .atom text { fill: #eef1fb; font: 700 17px var(--sans); text-anchor: middle; } #mol2d .atom .o { fill: #ff7a7f; }
#mol2d .chg text { fill: #9fbcff; font: 700 11px var(--mono); text-anchor: middle; }
#mol2d .hb { stroke: var(--mint); stroke-width: 3; stroke-dasharray: 3 6; stroke-linecap: round; fill: none; }
#mol2d .cap { fill: var(--mint); font: 700 10px var(--mono); text-anchor: middle; letter-spacing: .06em; text-transform: uppercase; }
#mol3d { display: block; width: 100%; height: 230px; cursor: grab; touch-action: none; }
#mol3d:active { cursor: grabbing; }
.mol-cap { margin: 0; padding: 6px 12px 10px; text-align: center; font: 500 .74rem var(--mono); color: var(--muted); }



/* INTERACTIVE CAROUSEL */
.ix .pill { margin-bottom: 0; }
.ix-stage { position: relative; aspect-ratio: 520 / 316; background: var(--diagram); border-radius: var(--r); overflow: hidden; }
.ix-stage svg, .ix-stage canvas { display: block; width: 100%; height: 100%; touch-action: none; }
.ix-stage svg.drag-x { cursor: ew-resize; user-select: none; }
.ix-controls { display: grid; gap: 12px; min-height: 136px; align-content: start; margin: 4px 0 0; }
.ix-slider { display: grid; grid-template-columns: 1fr auto; gap: 2px 12px; font-size: .88rem; font-weight: 600; color: var(--muted); }
.ix-slider output { color: var(--text); font: 700 .85rem var(--mono); }
.ix-slider input { grid-column: 1 / -1; width: 100%; accent-color: var(--blue); }
.ix-seg { display: inline-flex; border: 1px solid var(--line); border-radius: var(--r); overflow: hidden; justify-self: start; }
.ix-seg button { font: 700 .8rem var(--sans); color: var(--text-2); background: var(--surface-2); border: 0; padding: 7px 14px; cursor: pointer; }
.ix-seg button + button { border-left: 1px solid var(--line); }
.ix-seg button[aria-pressed="true"] { background: var(--blue); color: #fff; }
.ix-note { margin: 10px 0 0; min-height: 4.6em; padding: 10px 14px; font-size: .9rem; line-height: 1.5; color: var(--text-2); background: rgba(59, 107, 255, .1); border-left: 3px solid var(--blue); }
.ix-note b { color: #fff; }
.ix-nav { display: grid; gap: 10px; margin-top: 14px; }
.ix-tabs { display: grid; grid-template-columns: repeat(6, 1fr); gap: 4px; }
.ix-tabs button { font: 700 .66rem var(--mono); text-transform: uppercase; letter-spacing: .03em; color: var(--muted); background: transparent; border: 1px solid var(--line); border-radius: var(--r); padding: 7px 2px; cursor: pointer; white-space: nowrap; }
.ix-tabs button[aria-selected="true"] { color: #fff; background: rgba(59, 107, 255, .25); border-color: var(--blue); }
.ix-pn { display: flex; align-items: center; gap: 10px; }
.ix-arrow { font: 700 .9rem var(--sans); color: var(--text); background: var(--surface-2); border: 1px solid var(--line); border-radius: var(--r); padding: 10px 16px; cursor: pointer; }
.ix-arrow.next { background: var(--blue); border-color: var(--blue); color: #fff; padding-inline: 22px; }
.ix-arrow:hover { filter: brightness(1.15); }
.ix-count { flex: 1; text-align: center; font: 500 .75rem var(--mono); color: var(--muted); }
.ix .dg-read { min-height: 2.2em; }

/* physics */
.rf-air { fill: rgba(255, 255, 255, .02); } .rf-glass { fill: rgba(59, 107, 255, .16); }
.rf-lbl { fill: #8b93b3; font: 700 11px var(--mono); letter-spacing: .06em; } .rf-lbl.crit { fill: #ff9a90; }
.rf-iface { stroke: rgba(255, 255, 255, .45); stroke-width: 2; }
.rf-normal { stroke: rgba(255, 255, 255, .3); stroke-width: 1.5; stroke-dasharray: 5 6; }
.rf-ray { stroke-width: 3.5; stroke-linecap: round; }
.rf-ray.inc { stroke: #fff; } .rf-ray.ref { stroke: var(--blue-l); } .rf-ray.refl { stroke: var(--mint); }
.rf-crit { stroke: #ff6b5e; stroke-width: 2; stroke-dasharray: 4 5; }
.rf-arc { fill: none; stroke: #fff; stroke-width: 1.8; opacity: .8; } .rf-arc.r { stroke: var(--blue-l); }
.rf-ang { fill: #fff; font: italic 700 14px Georgia, serif; text-anchor: middle; } .rf-ang.r { fill: var(--blue-l); }

/* biology */
.en-body { stroke-width: 3; stroke-linejoin: round; fill: #3b6bff; stroke: #9fbcff; }
.en-lbl { fill: #fff; opacity: .8; font: 800 13px var(--mono); letter-spacing: .12em; }
.en-tag { fill: #8b93b3; font: 700 10px var(--mono); letter-spacing: .06em; text-transform: uppercase; }
.en-sub { fill: var(--mint); stroke: rgba(0, 0, 0, .35); stroke-width: 1.5; stroke-linejoin: round; }
.en-bad { fill: #ff6b5e; font: 800 22px var(--sans); }
.en-base { fill: none; stroke: rgba(255, 255, 255, .28); stroke-width: 1.5; stroke-dasharray: 4 5; }
.en-area { fill: rgba(59, 107, 255, .2); }
.en-curve { fill: none; stroke: var(--blue-l); stroke-width: 3.5; stroke-linejoin: round; }

/* economics */
.ec-d { stroke: var(--blue-l); stroke-width: 3.5; stroke-linecap: round; } .ec-s { stroke: var(--mint); stroke-width: 3.5; stroke-linecap: round; }
.ec-ghost { stroke: rgba(255, 255, 255, .25); stroke-width: 2; stroke-dasharray: 5 6; }
.ec-cs { fill: rgba(127, 166, 255, .22); } .ec-ps { fill: rgba(47, 213, 166, .2); }
.ec-t { font: 700 10px var(--mono); letter-spacing: .04em; text-transform: uppercase; } .ec-t.cs { fill: #a9c2ff; } .ec-t.ps { fill: #7fe9cb; }
.ec-lbl { font: 800 15px var(--display); } .ec-lbl.d { fill: var(--blue-l); } .ec-lbl.s { fill: var(--mint); } .ec-lbl.ghost { fill: #7a82a3; font-size: 12px; } .ec-lbl.p { fill: #fff; font: 700 12px var(--mono); }

/* computer science */
.bin { height: 100%; display: grid; grid-template-rows: auto auto auto auto; align-content: center; gap: 12px; padding: 14px 18px; }
.bin-big { text-align: center; }
.bin-big small { display: block; font: 700 .7rem var(--mono); text-transform: uppercase; letter-spacing: .1em; color: var(--muted); }
.bin-big b { font: 800 3.2rem/1 var(--display); letter-spacing: -.03em; }
.bin-row { display: grid; grid-template-columns: repeat(8, 1fr); gap: 8px; }
.bin-pv span { text-align: center; font: 700 .72rem var(--mono); color: var(--muted); }
.bin-bits button { aspect-ratio: 1; font: 800 1.4rem var(--mono); color: #55608a; background: #0a0d17; border: 2px solid #232a45; border-radius: var(--r); cursor: pointer; transition: background .12s, color .12s, box-shadow .12s; }
.bin-bits button.on { color: #fff; background: var(--blue); border-color: #9fbcff; box-shadow: 0 0 18px rgba(59, 107, 255, .6); }
.bin-act { grid-template-columns: repeat(4, auto); justify-content: center; }
.bin-act button { font: 700 .78rem var(--sans); color: var(--text); background: var(--surface-2); border: 1px solid var(--line); border-radius: var(--r); padding: 8px 12px; cursor: pointer; }
.bin-act button:hover { border-color: var(--blue); }


.tabs { display: flex; gap: 6px; border-bottom: 1px solid var(--line); }
.tabs button { flex: 1; font: 700 .85rem var(--sans); padding: 10px 8px; border: 0; border-radius: var(--r); background: transparent; color: var(--muted); cursor: pointer; }
.tabs button[aria-selected="true"] { background: rgba(59, 107, 255, .16); color: var(--blue-l); box-shadow: inset 0 -3px 0 var(--blue); }
.ms { list-style: none; padding: 0; margin: 10px 0 0; display: grid; gap: 8px; }
.ms label { display: flex; gap: 10px; align-items: flex-start; padding: 10px 12px; border-radius: var(--r); cursor: pointer; background: var(--surface-2); font-size: .95rem; }
.ms label:has(input:checked) { background: rgba(47, 213, 166, .16); }
.ms b { font: 700 .8rem var(--mono); background: var(--blue); color: #fff; padding: 1px 7px; border-radius: var(--r); }
.ms input { accent-color: var(--mint); width: 18px; height: 18px; margin-top: 3px; }
.score { font: 700 1.1rem var(--mono); margin: 16px 0 0; } .score b { color: var(--blue-l); font-size: 1.5rem; }
.tip { background: rgba(59, 107, 255, .1); border: 1px solid rgba(127, 166, 255, .3); border-radius: var(--r); padding: 12px 14px; font-size: .95rem; margin: 0 0 10px; color: var(--text-2); }
.tip b { color: #fff; }

/* TABLET */


/* SECTIONS */
.section { padding: 84px 0; }
.section.alt { background: #0d101a; border-block: 1px solid var(--line); }
.section.dark { background: var(--navy); border-top: 1px solid var(--line); }
.section.sun { background: var(--deep); border-block: 1px solid rgba(127, 166, 255, .2); }
.two { display: grid; grid-template-columns: 1.1fr .9fr; gap: 56px; align-items: center; }

/* TILES */
.tiles { list-style: none; padding: 0; margin: 0; display: grid; grid-template-columns: repeat(auto-fill, minmax(250px, 1fr)); gap: 18px; }
.tile { position: relative; background: var(--surface); border: 1px solid var(--line); border-radius: var(--r); padding: 22px; transition: transform .15s, border-color .15s; overflow: hidden; }
.tile:hover { transform: translateY(-4px); border-color: rgba(127, 166, 255, .5); }
.tile::after { content: ""; position: absolute; right: -20px; top: -20px; width: 70px; height: 80px; background: var(--c, var(--blue)); clip-path: polygon(50% 0, 100% 25%, 100% 75%, 50% 100%, 0 75%, 0 25%); opacity: .5; }
.tile:nth-child(4n+1) { --c: var(--blue); } .tile:nth-child(4n+2) { --c: var(--blue-l); } .tile:nth-child(4n+3) { --c: var(--coral); } .tile:nth-child(4n) { --c: var(--mint); }
.tile:nth-child(3n)::after { border-radius: var(--r); rotate: 20deg; }
.tile h3 { font: 800 1.25rem var(--display); margin: 14px 0 6px; letter-spacing: -.02em; }
.tile p { margin: 0; color: var(--muted); font-size: .95rem; }
.tag { display: inline-block; position: relative; z-index: 1; font: 700 .68rem var(--mono); text-transform: uppercase; letter-spacing: .06em; padding: 4px 10px; border-radius: var(--r); background: rgba(47, 213, 166, .16); color: #6ff0c8; }
.tag.pro { background: var(--blue); color: #fff; }
.tag.both { background: rgba(59, 107, 255, .2); color: var(--blue-l); }

/* ORIGINALS */
.checks { list-style: none; padding: 0; margin: 0 0 30px; display: grid; gap: 14px; }
.checks li { padding-left: 36px; position: relative; color: var(--text-2); }
.checks li::before { content: "✓"; position: absolute; left: 0; top: -1px; width: 26px; height: 26px; display: grid; place-items: center; background: var(--blue); color: #fff; font-weight: 800; border-radius: var(--r); }
.checks b { color: #fff; }
.pred { background: #fff; color: var(--on-light); border-radius: var(--r); padding: 26px; box-shadow: 0 28px 70px rgba(0, 0, 0, .5); rotate: 1.5deg; }
.pred-top { display: flex; justify-content: space-between; align-items: center; margin: 0 0 8px; font: 700 .8rem var(--mono); }
.stamp { color: var(--coral); box-shadow: inset 0 0 0 3px var(--coral); padding: 3px 12px; border-radius: var(--r); text-transform: uppercase; rotate: -3deg; font-size: .88rem; }
.pred h3 { font-size: 1.9rem; margin-bottom: 14px; }
.pred ul { list-style: none; margin: 0 0 12px; padding: 0; }
.pred li { display: flex; gap: 12px; padding: 12px 0; border-top: 1px solid rgba(20, 18, 43, .12); align-items: center; }
.pred li span { font: 700 .82rem var(--mono); background: var(--deep); color: #fff; padding: 2px 8px; border-radius: var(--r); }
.pred li em { margin-left: auto; font-style: normal; color: var(--blue-d); letter-spacing: 2px; }
.pred .blurred { filter: blur(4px); user-select: none; }
.pred .micro { color: #5d5b78; }

/* LAB */
.lab-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 24px; }
.card { background: var(--surface); border: 1px solid var(--line); border-radius: var(--r); padding: 22px; box-shadow: var(--soft); }
.card header { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; }
.card h3 { font: 800 1.4rem var(--display); } .card h3 small { font: 500 .85rem var(--sans); color: var(--muted); margin-left: 6px; letter-spacing: 0; }
.card svg { display: block; width: 100%; height: auto; background: var(--diagram); border-radius: var(--r); margin: 16px 0; }
.controls { display: grid; gap: 12px; }
.controls label { display: grid; grid-template-columns: 1fr auto; gap: 4px 12px; font-size: .9rem; color: var(--muted); font-weight: 600; }
.controls output { color: var(--text); font: 700 .9rem var(--mono); }
.controls input[type=range] { grid-column: 1 / -1; width: 100%; accent-color: var(--blue); }
.readout { display: flex; gap: 12px; align-items: baseline; margin: 14px 0 0; font: 500 .85rem var(--mono); color: var(--muted); }
.readout b { font: 800 1.5rem var(--display); color: var(--text); }
.readout small { margin-left: auto; font-size: .78rem; }
#circuit .bg { fill: var(--diagram); }
.wire { fill: none; stroke: #303650; stroke-width: 4; stroke-linejoin: round; }
.flow { fill: none; stroke: var(--hl); stroke-width: 4.5; stroke-linecap: round; stroke-dasharray: 1 20; animation: flow var(--dur, 1s) linear infinite; }
@keyframes flow { to { stroke-dashoffset: -21; } }
.batt { stroke: #fff; stroke-width: 4; } .batt.short { stroke-width: 7; }
.zig { fill: none; stroke: #fff; stroke-width: 3; stroke-linejoin: round; }
.lbl { fill: #858dae; font: 12px var(--mono); }
.glow { fill: var(--hl); opacity: var(--glow, .5); filter: blur(10px); }
.bulb { fill: #1d1838; stroke: var(--hl); stroke-width: 3; }
.bulb-x { stroke: var(--hl); stroke-width: 2; opacity: var(--bulb, .8); }
.at-shell { fill: none; stroke: #363d5c; stroke-width: 1.8; }
.at-e { fill: var(--blue-l); stroke: var(--diagram); stroke-width: 2; }
.at-n { fill: var(--coral); stroke: var(--diagram); stroke-width: 2; }
.at-txt { fill: #fff; font: 700 11px var(--mono); text-anchor: middle; }
.lib-label { margin: 40px 0 12px; font: 700 1rem var(--sans); }
.lib { list-style: none; padding: 0; margin: 0; display: flex; flex-wrap: wrap; gap: 10px; }
.lib li { padding: 8px 16px; border-radius: var(--r); font-size: .9rem; font-weight: 600; background: var(--surface); border: 1px solid var(--line); color: var(--text-2); }
.lib li::before { content: "🔒 "; font-size: .72rem; }

/* NOTES */
.notes-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 24px; }
.note { background: var(--surface); border: 1px solid var(--line); border-radius: var(--r); padding: 30px; box-shadow: var(--soft); }
.note.gold { background: var(--surface); border-color: rgba(127, 166, 255, .3); }
.note header { margin-bottom: 18px; }
.note header div { display: flex; align-items: center; gap: 12px; margin-bottom: 4px; }
.note header h3 { font-size: 2.1rem; }
.note header p { margin: 0; color: var(--muted); }
.note h4 { font: 800 1.15rem var(--display); margin-bottom: 10px; letter-spacing: -.01em; }
.note ul { padding-left: 1.1rem; margin: 0 0 16px; } .note li { margin-bottom: 8px; color: var(--text-2); }
.note p { color: var(--text-2); }
code { font: 500 .88em var(--mono); background: rgba(255, 255, 255, .09); padding: 1px 6px; border-radius: var(--r); color: var(--text); }
.textlink { font-weight: 700; color: var(--blue-l); text-decoration-thickness: 2px; text-underline-offset: 4px; }
.locked { position: relative; border-radius: var(--r); padding: 14px; min-height: 180px; display: grid; background: var(--diagram); border: 1px dashed rgba(127, 166, 255, .4); }
.blur { filter: blur(5px); user-select: none; }
.locked .btn { position: absolute; top: 50%; left: 50%; translate: -50% -50%; white-space: nowrap; }

/* TUTORS */
.filters, .billing { display: flex; gap: 8px; flex-wrap: wrap; margin-bottom: 24px; }
.billing { margin-top: 24px; }
.chip { font: 700 .88rem var(--sans); cursor: pointer; background: var(--surface); color: var(--text-2); border: 1px solid var(--line); border-radius: var(--r); padding: 9px 18px; }
.chip[aria-pressed="true"] { background: var(--blue); border-color: var(--blue); color: #fff; }
.save { background: var(--mint); color: var(--on-light); border-radius: var(--r); padding: 1px 8px; margin-left: 4px; font: 700 .7rem var(--mono); }
.tutor-grid { list-style: none; margin: 0; padding: 0; display: grid; grid-template-columns: repeat(auto-fill, minmax(210px, 1fr)); gap: 18px; }
.tcard { --accent: var(--blue-l); display: flex; flex-direction: column; width: 100%; height: 100%; text-align: left; color: var(--text); cursor: pointer; background: var(--surface); border: 1px solid var(--line); border-radius: var(--r); padding: 0; overflow: hidden; transition: transform .15s, border-color .15s, box-shadow .15s; }
.tcard:hover, .tcard:focus-visible { transform: translateY(-5px); border-color: var(--accent); box-shadow: 0 18px 44px rgba(0, 0, 0, .5); }
.tcard .stage { height: 124px; display: grid; place-items: center; background: var(--accent); }
.tcard .stage img { height: 92px; width: auto; filter: drop-shadow(0 6px 0 rgba(10, 10, 30, .22)); }
.tcard .awake { display: none; }
.tcard:hover .awake, .tcard:focus-visible .awake { display: block; }
.tcard:hover .rest, .tcard:focus-visible .rest { display: none; }
.tcard .body { padding: 16px 18px 20px; display: flex; flex-direction: column; flex: 1; }
.tcard .subj { font: 700 .7rem var(--mono); text-transform: uppercase; letter-spacing: .06em; color: var(--blue-l); }
.tcard h3 { font: 800 1.25rem var(--display); margin: 3px 0 4px; letter-spacing: -.02em; }
.tcard .tag-line { font-size: .88rem; color: var(--muted); margin: 0; line-height: 1.45; }

/* PRICING */
.plans { display: grid; grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); gap: 28px; max-width: 800px; margin-top: 8px; }
.plan { position: relative; background: rgba(255, 255, 255, .04); border: 1px solid var(--line); border-radius: var(--r); padding: 30px; display: flex; flex-direction: column; gap: 16px; }
.plan h3 { font-size: 1.7rem; }
.price { font: 800 3.2rem var(--display); margin: 0; letter-spacing: -.03em; } .price small { font: 500 .9rem var(--sans); color: var(--muted); letter-spacing: 0; }
.plan ul { list-style: none; padding: 0; margin: 4px 0 0; display: grid; gap: 10px; }
.plan li { padding-left: 28px; position: relative; color: var(--text-2); font-size: .98rem; }
.plan li::before { content: "✓"; position: absolute; left: 0; color: var(--mint); font-weight: 800; }
.plan.best { background: var(--deep); border-color: rgba(127, 166, 255, .6); box-shadow: 0 0 0 2px var(--blue); }
.plan.best .price small { color: #c3d4ff; } .plan.best li { color: #e6eeff; } .plan.best li::before { color: #fff; }
.ribbon { position: absolute; top: -15px; right: 22px; background: #fff; color: var(--on-light); font: 700 .72rem var(--mono); text-transform: uppercase; padding: 5px 12px; border-radius: var(--r); }

/* FAQ */
details { border-bottom: 1px solid var(--line); padding: 20px 0; }
details:first-of-type { border-top: 1px solid var(--line); margin-top: 28px; }
summary { cursor: pointer; font: 700 1.2rem var(--display); letter-spacing: -.01em; list-style: none; display: flex; justify-content: space-between; gap: 16px; }
summary::after { content: "+"; font: 700 1.5rem var(--mono); line-height: 1; color: var(--blue-l); }
details[open] summary::after { content: "−"; }
details p { margin: 12px 0 0; color: var(--text-2); max-width: 62ch; }

/* FINAL */
.final { position: relative; overflow: hidden; background: var(--blue-d); padding: 96px 0; text-align: center; isolation: isolate; border-top: 1px solid var(--line); }
.final img { filter: drop-shadow(0 6px 0 rgba(10, 10, 30, .35)); animation: bob 2.4s steps(4) infinite; }
@keyframes bob { 50% { transform: translateY(-8px); } }
.final h2 { max-width: none; margin: 16px 0 10px; font-size: clamp(2.3rem, 5.2vw, 3.8rem); }
.final p { margin: 0 0 28px; font-size: 1.15rem; color: #dce6ff; }
.foot { padding: 36px 0 90px; background: #04050a; border-top: 1px solid var(--line); } .foot p { margin: 0 0 6px; }
.mobile-cta { display: none; }

/* DIALOGS */
dialog { color: var(--text); }
dialog::backdrop { background: rgba(5, 5, 10, .72); backdrop-filter: blur(4px); }
.modal { width: min(420px, 100% - 24px); margin: auto; padding: 30px; border: 1px solid var(--line); border-radius: var(--r); background: var(--surface); box-shadow: 0 30px 80px rgba(0, 0, 0, .7); }
.modal h3 { font-size: 1.8rem; margin-bottom: 6px; }
.modal p { color: var(--text-2); }
.modal form[method=dialog].x { position: absolute; top: 14px; right: 14px; } .x button { border: 0; background: var(--surface-2); color: var(--text); border-radius: var(--r); width: 34px; height: 34px; cursor: pointer; font-weight: 700; }
.modal label { display: grid; gap: 6px; font: 700 .7rem var(--mono); text-transform: uppercase; color: var(--muted); margin: 16px 0; }
.modal input[type=email], .modal input[type=password] { font: 500 1rem var(--sans); border: 1px solid var(--line); border-radius: var(--r); padding: 14px; background: var(--surface-2); color: var(--text); text-transform: none; }
.modal .btn + .btn, .modal button + .btn { margin-top: 12px; }

.chat { width: min(560px, 100% - 24px); height: min(720px, 100% - 24px); margin: auto; padding: 0; border: 1px solid var(--line); border-radius: var(--r); background: var(--surface); overflow: hidden; box-shadow: 0 30px 80px rgba(0, 0, 0, .7); }
.chat[open] { display: flex; flex-direction: column; }
.chat-head { --accent: var(--blue-l); display: flex; align-items: center; gap: 14px; padding: 14px 18px; background: var(--accent); color: var(--on-light); }
.chat-head img { height: 48px; width: auto; filter: drop-shadow(0 4px 0 rgba(10, 10, 30, .2)); }
.who { flex: 1; min-width: 0; } .who h3 { font-size: 1.3rem; } .who p { margin: 0; font: 700 .72rem var(--mono); text-transform: uppercase; }
.icon-btn { width: 36px; height: 36px; border-radius: var(--r); border: 0; background: rgba(255, 255, 255, .85); color: var(--on-light); font-weight: 700; cursor: pointer; }
.profile { padding: 12px 18px; font-size: .9rem; background: var(--surface-2); color: var(--text-2); } .profile[hidden] { display: none; } .profile p { margin: 0 0 6px; }
.switch-row { display: grid; grid-template-columns: auto 1fr; gap: 8px 10px; align-items: center; padding: 10px 18px; border-bottom: 1px solid var(--line); font: 500 .8rem var(--mono); color: var(--text-2); }
.switch-row select { font: 600 .88rem var(--sans); background: var(--surface-2); border: 1px solid var(--line); border-radius: var(--r); padding: 7px 10px; color: var(--text); }
.quota { grid-column: 1 / -1; display: flex; align-items: center; gap: 10px; }
.quota .bar { flex: 1; height: 8px; border-radius: var(--r); background: var(--surface-2); overflow: hidden; }
.quota .bar i { display: block; height: 100%; width: 100%; background: var(--blue); border-radius: var(--r); transition: width .3s; }
.log { flex: 1; overflow-y: auto; padding: 16px; display: flex; flex-direction: column; gap: 10px; background: var(--bg); }
.msg { max-width: 85%; padding: 11px 15px; border-radius: var(--r); font-size: .95rem; line-height: 1.5; white-space: pre-wrap; }
.msg.bot { align-self: flex-start; background: var(--surface-2); border-bottom-left-radius: var(--r); }
.msg.me { align-self: flex-end; background: var(--blue); color: #fff; border-bottom-right-radius: var(--r); }
.msg.note { align-self: center; max-width: 100%; background: none; color: var(--muted); font-size: .8rem; text-align: center; }
.msg.wall { align-self: stretch; max-width: 100%; text-align: center; background: rgba(127, 166, 255, .1); border: 1px solid rgba(127, 166, 255, .3); }
.typing span { display: inline-block; width: 7px; height: 7px; margin-right: 3px; border-radius: 50%; background: var(--muted); animation: dot 1s infinite; }
.typing span:nth-child(2) { animation-delay: .15s; } .typing span:nth-child(3) { animation-delay: .3s; }
@keyframes dot { 50% { transform: translateY(-4px); opacity: .4; } }
.qchips { display: flex; gap: 6px; flex-wrap: wrap; padding: 8px 16px; background: var(--bg); }
.qchips button { font: 600 .8rem var(--sans); background: var(--surface-2); color: var(--text-2); border: 0; border-radius: var(--r); padding: 6px 13px; cursor: pointer; }
.qchips button:hover { background: var(--blue); color: #fff; }
.chat-form { display: flex; gap: 8px; padding: 12px 16px; border-top: 1px solid var(--line); }
.chat-form input { flex: 1; min-width: 0; font: inherit; color: var(--text); background: var(--surface-2); border: 1px solid var(--line); border-radius: var(--r); padding: 11px 16px; }
.chat-form input:disabled { opacity: .5; }
.reset { background: none; border: 0; color: var(--muted); font: .75rem var(--sans); padding: 0 0 10px; cursor: pointer; text-decoration: underline; }

/* RESPONSIVE */
@media (max-width: 1000px) {
  .hero-copy { position: static; }
  .hero-top { grid-template-columns: 1fr; gap: 40px; }
}
@media (max-width: 1000px) { .tablet-wrap { padding-right: 0; } .pencil { display: none; } }
@media (max-width: 900px) {
  .screen { grid-template-columns: 1fr; } .screen::after { display: none; } .t-paper { border-bottom: 1px solid #263055; }
  .split, .two, .lab-grid, .notes-grid { grid-template-columns: 1fr; }
  .paper { border-right: 0; border-bottom: 1px solid var(--line); }
  .nav nav { display: none; } .nav-right { margin-left: auto; }
  .section { padding: 68px 0; }
  .pred { rotate: 0deg; }
  .mobile-cta { display: block; position: fixed; inset: auto 0 0; z-index: 25; padding: 10px 16px; background: rgba(11, 11, 15, .95); border-top: 1px solid var(--line); }
  .mobile-cta .btn { width: 100%; }
  .win-title { display: none; } .diff { margin-left: auto; }
}
@media (max-width: 760px) { .sc-row { grid-template-columns: 1fr; } }
@media (max-width: 560px) {
  .nav .meter { display: none; }
  .picker .btn { width: 100%; }
  .sc-tutors .sc-text { width: 58%; }
  .reel { padding-left: 56%; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .reel, .final img, .flow { animation: none; }
  .btn, .tile, .tcard, .sc-tutors, .sc-labs { transition: none; }
}

/* AUTH */
.nav-user { display: flex; align-items: center; gap: 10px; font-size: .85rem; color: var(--text-2); }
.nav-user #navEmail { max-width: 160px; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.suMode { margin: 14px 0 0; }
.auth-msg { margin: 0 0 12px; padding: 10px 12px; font-size: .9rem; color: #ffc2bc; background: rgba(255, 107, 94, .12); border-left: 3px solid var(--coral); }
.auth-msg.ok { color: #b6f5e3; background: rgba(47, 213, 166, .12); border-color: var(--mint); }
@media (max-width: 900px) { .nav-user #navEmail { display: none; } #navLogin { display: none; } }

/* TUTOR REPLIES (rendered Markdown) */
.msg.bot:not(.typing) { white-space: normal; }
.msg.bot > :first-child { margin-top: 0; } .msg.bot > :last-child { margin-bottom: 0; }
.msg.bot p { margin: 0 0 .6em; }
.msg.bot h3, .msg.bot h4 { font: 800 1.02rem var(--display); letter-spacing: -.01em; margin: .9em 0 .35em; }
.msg.bot strong { color: #fff; }
.msg.bot ul, .msg.bot ol { margin: 0 0 .6em; padding-left: 1.3em; } .msg.bot li { margin: .15em 0; }
.msg.bot hr { border: 0; border-top: 1px solid var(--line); margin: .8em 0; }
.msg.bot code { font: 500 .85em var(--mono); background: rgba(255, 255, 255, .1); padding: 1px 5px; }
.msg.bot pre { margin: 0 0 .6em; padding: 10px 12px; overflow-x: auto; background: var(--diagram); } .msg.bot pre code { background: none; padding: 0; }
.msg.bot blockquote { margin: 0 0 .6em; padding: 4px 12px; border-left: 3px solid var(--blue); color: var(--text-2); }
.msg.bot .md-table { overflow-x: auto; margin: 0 0 .6em; }
.msg.bot table { border-collapse: collapse; font-size: .88rem; }
.msg.bot th, .msg.bot td { border: 1px solid var(--line); padding: 5px 9px; text-align: left; } .msg.bot th { background: rgba(255, 255, 255, .06); }
.fu { display: flex; flex-wrap: wrap; gap: 6px; align-items: center; align-self: flex-start; max-width: 100%; }
.fu span { font: 700 .66rem var(--mono); text-transform: uppercase; letter-spacing: .08em; color: var(--muted); margin-right: 2px; }
.fu button { font: 600 .82rem var(--sans); text-align: left; color: var(--text); background: rgba(59, 107, 255, .14); border: 1px solid rgba(127, 166, 255, .45); padding: 7px 12px; cursor: pointer; border-radius: var(--r); }
.fu button:hover { background: var(--blue); border-color: var(--blue); color: #fff; }