:root {
  color-scheme: dark;
  --bg: #090a0c;
  --panel: #101216;
  --panel-2: #15181d;
  --line: #252a31;
  --line-soft: #1d2127;
  --text: #f2f4f7;
  --muted: #929aa6;
  --faint: #626b77;
  --accent: #b8f26b;
  --accent-deep: #7ba637;
  --accent-wash: rgba(184, 242, 107, 0.1);
  --blue: #7cb8ff;
  --blue-wash: rgba(124, 184, 255, 0.1);
  --danger: #ff756f;
  --danger-wash: rgba(255, 117, 111, 0.1);
  --warning: #f8c15c;
  --mono: "Cascadia Code", "SFMono-Regular", Consolas, monospace;
  --sans: Inter, Pretendard, "Noto Sans KR", system-ui, -apple-system, sans-serif;
}

* { box-sizing: border-box; }

html, body { margin: 0; min-height: 100%; background: var(--bg); color: var(--text); }

body {
  font-family: var(--sans);
  background-image:
    radial-gradient(circle at 80% 0%, rgba(124, 184, 255, 0.045), transparent 28rem),
    radial-gradient(circle at 10% 100%, rgba(184, 242, 107, 0.035), transparent 32rem);
}

button, select, input, textarea { font: inherit; }
button, select, input[type="range"] { cursor: pointer; }
button:focus-visible, select:focus-visible, input:focus-visible, textarea:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 3px;
}

.app-shell { min-height: 100dvh; display: grid; grid-template-rows: 72px 1fr; }

.topbar {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  gap: 24px;
  padding: 0 clamp(20px, 4vw, 64px);
  border-bottom: 1px solid var(--line-soft);
  background: rgba(9, 10, 12, 0.82);
  backdrop-filter: blur(16px);
  position: relative;
  z-index: 10;
}

.brand { display: inline-flex; width: fit-content; align-items: center; gap: 11px; color: var(--text); text-decoration: none; font-size: 14px; font-weight: 700; letter-spacing: -.02em; }
.brand-mark { width: 29px; height: 29px; display: grid; place-items: center; border: 1px solid #3a414b; border-radius: 8px; font-family: var(--mono); color: var(--accent); background: var(--panel-2); }
.site-tabs { display: flex; align-items: center; gap: 3px; padding: 4px; border: 1px solid var(--line-soft); border-radius: 12px; background: rgba(13,15,18,.8); }
.site-tabs a { padding: 8px 13px; border-radius: 8px; color: var(--muted); text-decoration: none; font-size: 12px; font-weight: 650; transition: 160ms ease; }
.site-tabs a:hover { color: var(--text); }
.site-tabs a.active { color: #11150d; background: var(--accent); }
.top-actions { justify-self: end; display: flex; align-items: center; gap: 9px; }
.top-actions.document-mode .concept-nav,
.top-actions.document-mode .soundless-hint { display: none; }
.concept-nav { display: flex; align-items: center; gap: 8px; }
.icon-button, .soundless-hint, .secondary-button, .segmented button, .action-button {
  border: 1px solid var(--line);
  background: var(--panel);
  color: var(--muted);
  transition: 160ms ease;
}
.icon-button { width: 36px; height: 36px; border-radius: 10px; }
.icon-button:hover, .soundless-hint:hover, .secondary-button:hover { color: var(--text); border-color: #414954; transform: translateY(-1px); }
.concept-picker select { min-width: 230px; height: 40px; padding: 0 38px 0 14px; color: var(--text); border: 1px solid var(--line); border-radius: 11px; background: var(--panel); font-size: 14px; font-weight: 650; }
.soundless-hint { justify-self: end; padding: 8px 12px; border-radius: 9px; font-size: 12px; }

.concept-stage { min-height: 0; padding: clamp(28px, 4vh, 48px) clamp(20px, 5vw, 80px) 40px; }
.concept-stage:focus { outline: none; }
.concept-screen { max-width: 1380px; min-height: calc(100dvh - 160px); margin: 0 auto; display: grid; grid-template-columns: minmax(280px, .78fr) minmax(560px, 1.5fr); gap: clamp(28px, 5vw, 76px); align-items: center; animation: screen-in 350ms cubic-bezier(.2,.75,.25,1); }
@keyframes screen-in { from { opacity: 0; transform: translateY(8px); } }

.lesson-copy { align-self: center; max-width: 460px; }
.eyebrow { margin: 0 0 17px; color: var(--accent); font-family: var(--mono); font-size: 12px; letter-spacing: .08em; }
.lesson-copy h1 { margin: 0; font-size: clamp(36px, 4vw, 64px); line-height: 1.02; letter-spacing: -.055em; font-weight: 760; }
.lesson-copy h1 small { display: block; margin-top: 13px; color: var(--muted); font-size: .35em; line-height: 1.4; letter-spacing: -.025em; font-weight: 520; }
.lead { margin: 24px 0 0; color: #b5bcc5; font-size: clamp(15px, 1.3vw, 18px); line-height: 1.8; word-break: keep-all; }
.core-note { margin-top: 26px; padding: 16px 0 0 18px; border-left: 2px solid var(--accent); color: var(--muted); font-size: 13px; line-height: 1.7; }
.core-note strong { display: block; margin-bottom: 3px; color: var(--text); font-size: 13px; }

.lab { min-width: 0; border: 1px solid var(--line); border-radius: 24px; overflow: hidden; background: rgba(16,18,22,.92); box-shadow: 0 30px 80px rgba(0,0,0,.24); }
.lab-head { min-height: 54px; padding: 0 18px 0 22px; display: flex; align-items: center; justify-content: space-between; gap: 14px; border-bottom: 1px solid var(--line-soft); }
.lab-title { display: flex; align-items: center; gap: 9px; color: var(--muted); font-size: 12px; font-weight: 650; }
.status-dot { width: 7px; height: 7px; border-radius: 50%; background: var(--accent); box-shadow: 0 0 0 4px var(--accent-wash); }
.lab-body { min-height: 500px; display: grid; grid-template-rows: 1fr auto; }
.visual-area { position: relative; min-height: 390px; padding: clamp(24px, 4vw, 48px); display: grid; align-content: center; background-image: linear-gradient(rgba(255,255,255,.018) 1px, transparent 1px), linear-gradient(90deg, rgba(255,255,255,.018) 1px, transparent 1px); background-size: 28px 28px; }
.controls { padding: 18px 22px; border-top: 1px solid var(--line-soft); background: #0d0f12; display: flex; flex-wrap: wrap; align-items: center; gap: 12px; }
.controls label { color: var(--muted); font-size: 12px; }
.controls-spacer { flex: 1; }

.segmented { display: inline-flex; padding: 3px; gap: 3px; border-radius: 11px; background: #08090b; border: 1px solid var(--line-soft); }
.segmented button { padding: 7px 11px; border: 0; border-radius: 8px; background: transparent; font-size: 12px; }
.segmented button.active { color: #0d1009; background: var(--accent); font-weight: 750; }
.secondary-button, .action-button { padding: 9px 13px; border-radius: 10px; font-size: 12px; }
.action-button { border-color: var(--accent-deep); background: var(--accent); color: #12150d; font-weight: 750; }
.action-button:hover { filter: brightness(1.07); transform: translateY(-1px); }
.action-button.danger { border-color: #9b4543; background: var(--danger); }
.field { min-width: 110px; padding: 9px 11px; border: 1px solid var(--line); border-radius: 9px; color: var(--text); background: var(--panel-2); }
.range { width: min(190px, 30vw); accent-color: var(--accent); }
.value-chip { padding: 5px 9px; border-radius: 7px; font-family: var(--mono); color: var(--accent); background: var(--accent-wash); font-size: 12px; }

.code-card { padding: 17px 19px; border-radius: 14px; border: 1px solid var(--line); background: #0a0c0f; font: 13px/1.8 var(--mono); color: #cbd1d8; white-space: pre-wrap; }
.code-card .active-line { display: block; margin: 0 -10px; padding: 0 10px; border-radius: 5px; color: var(--text); background: var(--accent-wash); }
.syn { color: var(--blue); }.num { color: #f8c15c; }.str { color: #c5e88b; }.dim { color: var(--faint); }.err { color: var(--danger); }
.mono { font-family: var(--mono); }

.memory-row { display: flex; align-items: stretch; justify-content: center; gap: 6px; }
.memory-cell { position: relative; width: clamp(62px, 8vw, 84px); min-height: 88px; padding: 20px 8px 10px; display: grid; place-items: center; border: 1px solid #333a43; border-radius: 12px; background: #12151a; font-family: var(--mono); transition: 180ms ease; }
.memory-cell .address { position: absolute; top: -21px; left: 50%; translate: -50% 0; color: var(--faint); font-size: 10px; }
.memory-cell .index { position: absolute; bottom: -23px; color: var(--faint); font-size: 10px; }
.memory-cell .cell-label { position: absolute; top: 7px; left: 9px; color: var(--muted); font: 10px var(--sans); }
.memory-cell .cell-value { font-size: 19px; font-weight: 700; }
.memory-cell.active { border-color: var(--accent); background: var(--accent-wash); transform: translateY(-5px); box-shadow: 0 9px 24px rgba(0,0,0,.25); }
.memory-cell.active .cell-value { color: var(--accent); }
.memory-cell.danger { border-color: var(--danger); background: var(--danger-wash); }
.memory-cell.ghost { border-style: dashed; color: var(--danger); background: rgba(255,117,111,.04); }
.pointer-arrow { height: 74px; display: grid; place-items: center; color: var(--accent); font: 12px var(--mono); }
.pointer-line { width: 2px; height: 46px; background: var(--accent); position: relative; }
.pointer-line::after { content: ""; position: absolute; bottom: -1px; left: -4px; width: 8px; height: 8px; border-right: 2px solid var(--accent); border-bottom: 2px solid var(--accent); rotate: 45deg; }
.readout { display: flex; align-items: center; justify-content: center; gap: 10px; color: var(--muted); font-size: 13px; text-align: center; }
.readout strong { color: var(--text); font-family: var(--mono); }
.equals { color: var(--faint); font: 22px var(--mono); }

.stack { display: grid; gap: 8px; width: min(430px, 100%); margin: 0 auto; }
.stack-frame { padding: 14px 17px; border: 1px solid var(--line); border-radius: 12px; background: var(--panel-2); display: flex; align-items: center; justify-content: space-between; gap: 14px; transition: 180ms ease; }
.stack-frame.active { border-color: var(--accent); background: var(--accent-wash); }
.stack-name { font: 12px var(--mono); color: var(--muted); }
.stack-vars { font: 13px var(--mono); }
.scope-pill { padding: 4px 7px; color: var(--blue); background: var(--blue-wash); border-radius: 6px; font-size: 10px; }

.type-grid { display: grid; grid-template-columns: repeat(3,1fr); gap: 10px; }
.type-card { min-height: 100px; padding: 15px; border: 1px solid var(--line); border-radius: 13px; background: var(--panel-2); transition: 160ms; }
.type-card.active { border-color: var(--accent); background: var(--accent-wash); }
.type-name { color: var(--blue); font: 13px var(--mono); }
.type-value { margin-top: 17px; font: 700 22px var(--mono); }
.type-size { margin-top: 7px; color: var(--faint); font-size: 10px; }

.flow-track { display: flex; align-items: center; justify-content: center; flex-wrap: wrap; gap: 8px; }
.flow-node { min-width: 86px; padding: 12px; text-align: center; border: 1px solid var(--line); border-radius: 11px; color: var(--muted); background: var(--panel-2); font: 12px var(--mono); transition: 180ms; }
.flow-node.active { color: var(--text); border-color: var(--accent); background: var(--accent-wash); transform: translateY(-3px); }
.flow-node.skipped { opacity: .28; text-decoration: line-through; }
.flow-edge { color: var(--faint); }

.string-editor { width: min(580px,100%); margin: 0 auto; display: grid; gap: 34px; }
.string-input { width: 100%; padding: 13px 15px; border: 1px solid var(--line); border-radius: 11px; background: var(--panel-2); color: var(--text); font: 16px var(--mono); }
.nul { color: var(--danger); font-size: 12px !important; }

.struct-card { width: min(410px,100%); margin: 0 auto; border: 1px solid var(--line); border-radius: 16px; overflow: hidden; background: var(--panel-2); }
.struct-head { padding: 12px 16px; border-bottom: 1px solid var(--line); color: var(--blue); font: 12px var(--mono); }
.struct-member { padding: 14px 16px; display: grid; grid-template-columns: 90px 1fr auto; gap: 14px; border-bottom: 1px solid var(--line-soft); font: 13px var(--mono); }
.struct-member:last-child { border-bottom: 0; }
.member-type { color: var(--faint); }.member-name { color: var(--muted); }.member-value { color: var(--accent); }

.heap { display: grid; grid-template-columns: repeat(8, 1fr); gap: 7px; width: min(560px,100%); margin: 0 auto; }
.heap-cell { aspect-ratio: 1; border: 1px dashed #353c45; border-radius: 8px; display: grid; place-items: center; color: var(--faint); font: 10px var(--mono); transition: 180ms; }
.heap-cell.used { border-style: solid; border-color: var(--accent); background: var(--accent-wash); color: var(--accent); }
.heap-cell.leaked { border-style: solid; border-color: var(--danger); background: var(--danger-wash); color: var(--danger); }

.file-paper { width: min(520px,100%); margin: 0 auto; border: 1px solid var(--line); border-radius: 14px; overflow: hidden; background: #f0eee6; color: #202226; box-shadow: 0 22px 55px rgba(0,0,0,.28); }
.file-tab { padding: 9px 14px; color: #6d6b64; border-bottom: 1px solid #d4d0c4; font: 11px var(--mono); }
.file-content { min-height: 140px; padding: 20px; font: 14px/1.8 var(--mono); white-space: pre-wrap; }
.file-cursor { background: #dbe9bf; }

.toast { position: fixed; left: 50%; bottom: 24px; z-index: 50; translate: -50% 12px; padding: 10px 14px; border: 1px solid var(--line); border-radius: 10px; color: var(--text); background: rgba(20,23,28,.96); opacity: 0; pointer-events: none; font-size: 12px; transition: 180ms; box-shadow: 0 12px 36px rgba(0,0,0,.3); }
.toast.show { opacity: 1; translate: -50% 0; }
.sr-only { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0,0,0,0); white-space: nowrap; border: 0; }

.document-screen { max-width: 1120px; margin: 0 auto; animation: screen-in 350ms cubic-bezier(.2,.75,.25,1); }
.document-hero { padding: clamp(34px, 6vw, 72px) 0 34px; border-bottom: 1px solid var(--line); }
.document-kicker { margin: 0 0 12px; color: var(--accent); font: 12px var(--mono); letter-spacing: .08em; }
.document-hero h1 { margin: 0; font-size: clamp(40px, 6vw, 72px); line-height: 1; letter-spacing: -.055em; }
.document-summary { max-width: 700px; margin: 18px 0 0; color: var(--muted); line-height: 1.8; word-break: keep-all; }
.document-jumps { position: sticky; top: 0; z-index: 4; display: flex; gap: 7px; overflow-x: auto; padding: 14px 0; background: linear-gradient(var(--bg) 75%, transparent); scrollbar-width: none; }
.document-jumps::-webkit-scrollbar { display: none; }
.document-jumps button { flex: 0 0 auto; padding: 8px 11px; border: 1px solid var(--line); border-radius: 9px; color: var(--muted); background: var(--panel); font-size: 11px; }
.document-jumps button:hover { color: var(--text); border-color: #414954; }
.markdown-body { max-width: 860px; margin: 0 auto; padding: 34px 0 100px; color: #c6cbd2; font-size: 15px; line-height: 1.8; }
.markdown-body > h1:first-child { display: none; }
.markdown-body h2 { scroll-margin-top: 76px; margin: 64px 0 22px; padding-top: 10px; color: var(--text); font-size: 28px; line-height: 1.3; letter-spacing: -.035em; }
.markdown-body h2:first-of-type { margin-top: 14px; }
.markdown-body h3 { margin: 38px 0 14px; color: var(--text); font-size: 19px; }
.markdown-body p { margin: 0 0 16px; }
.markdown-body strong { color: var(--text); }
.markdown-body code { padding: 2px 6px; border: 1px solid var(--line); border-radius: 5px; color: var(--accent); background: var(--accent-wash); font: .88em var(--mono); }
.markdown-body pre { margin: 18px 0; padding: 20px; overflow-x: auto; border: 1px solid var(--line); border-radius: 14px; background: #090b0e; color: #d3d8de; font: 12px/1.8 var(--mono); }
.markdown-body pre code { padding: 0; border: 0; color: inherit; background: none; font: inherit; }
.markdown-body ul, .markdown-body ol { margin: 13px 0 24px; padding-left: 23px; }
.markdown-body li { margin: 7px 0; padding-left: 5px; }
.markdown-body li::marker { color: var(--accent); font-family: var(--mono); }
.markdown-body blockquote { margin: 22px 0; padding: 13px 18px; border-left: 2px solid var(--blue); color: #b9c9dc; background: var(--blue-wash); }
.markdown-body hr { margin: 48px 0; border: 0; border-top: 1px solid var(--line); }
.markdown-body details { margin: 22px 0 48px; border: 1px solid var(--line); border-radius: 14px; background: var(--panel); overflow: hidden; }
.markdown-body summary { padding: 14px 18px; color: var(--muted); cursor: pointer; font-size: 12px; font-weight: 700; list-style: none; user-select: none; }
.markdown-body summary::-webkit-details-marker { display: none; }
.markdown-body summary::before { content: "+"; display: inline-grid; width: 18px; margin-right: 8px; place-items: center; color: var(--accent); font: 15px var(--mono); }
.markdown-body details[open] summary { border-bottom: 1px solid var(--line); color: var(--text); }
.markdown-body details[open] summary::before { content: "−"; }
.markdown-body details pre { margin: 0; border: 0; border-radius: 0; }
.markdown-body a { color: var(--blue); }
.document-loading { min-height: 55vh; display: grid; place-items: center; color: var(--muted); font-size: 13px; }
.document-error { margin-top: 44px; padding: 20px; border: 1px solid rgba(255,117,111,.4); border-radius: 12px; color: var(--danger); background: var(--danger-wash); }

/* Focused learning layout */
.concept-stage { padding: 26px clamp(24px, 5vw, 72px) 30px; }
.concept-screen {
  min-height: calc(100dvh - 128px);
  grid-template-columns: 1fr;
  grid-template-rows: auto minmax(0, 1fr);
  gap: 18px;
  align-items: stretch;
}
.lesson-copy {
  max-width: none;
  display: flex;
  align-items: end;
  justify-content: space-between;
  gap: 36px;
}
.lesson-copy .eyebrow { margin: 0 0 7px; }
.lesson-copy h1 { font-size: clamp(30px, 3.1vw, 46px); line-height: 1; }
.concept-rule { max-width: 560px; margin: 0 0 2px; color: #aab1ba; font-size: 13px; line-height: 1.55; text-align: right; word-break: keep-all; }
.concept-rule span { display: inline-block; margin-right: 8px; padding: 3px 7px; border-radius: 5px; color: var(--accent); background: var(--accent-wash); font: 10px var(--mono); }
.lab { border-radius: 20px; box-shadow: 0 24px 70px rgba(0,0,0,.2); }
.lab-head { min-height: 48px; padding: 0 18px; }
.lab-hint { color: var(--faint); font-size: 11px; }
.lab-body { min-height: 0; height: calc(100dvh - 278px); grid-template-rows: minmax(0, 1fr) auto; }
.visual-area { min-height: 0; padding: clamp(24px, 3.3vw, 44px); }
.controls { min-height: 64px; padding: 12px 18px; }
.code-card { border-color: #20252b; color: #b9c0c8; }
.memory-cell { width: clamp(68px, 8vw, 92px); }

/* Focused resources */
.resource-screen { max-width: 1180px; min-height: calc(100dvh - 128px); margin: 0 auto; display: grid; grid-template-rows: auto auto minmax(0,1fr); gap: 18px; animation: screen-in 320ms ease; }
.resource-header { display: flex; align-items: end; justify-content: space-between; gap: 40px; padding: 4px 0 16px; border-bottom: 1px solid var(--line-soft); }
.resource-kicker { margin: 0 0 6px; color: var(--accent); font: 10px var(--mono); letter-spacing: .08em; }
.resource-header h1 { margin: 0; font-size: clamp(30px, 4vw, 46px); line-height: 1; letter-spacing: -.05em; }
.resource-header > p { max-width: 420px; margin: 0 0 2px; color: var(--muted); font-size: 13px; text-align: right; }
.category-rail { display: grid; grid-template-columns: repeat(10, minmax(72px,1fr)); gap: 7px; }
.category-rail button { min-width: 0; padding: 10px 7px; border: 1px solid var(--line); border-radius: 10px; color: var(--muted); background: var(--panel); font-size: 10px; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; transition: 160ms ease; }
.category-rail button span { display: block; margin-bottom: 3px; color: var(--faint); font: 9px var(--mono); }
.category-rail button:hover { color: var(--text); border-color: #424a54; transform: translateY(-1px); }
.category-rail button.active { border-color: var(--accent-deep); color: #11150d; background: var(--accent); font-weight: 750; }
.category-rail button.active span { color: #4d631f; }
.question-workspace { min-height: 0; display: grid; grid-template-columns: 210px 1fr; border: 1px solid var(--line); border-radius: 20px; overflow: hidden; background: var(--panel); }
.question-toolbar { padding: 22px 18px; border-right: 1px solid var(--line); background: #0d0f12; }
.question-toolbar > div { display: grid; gap: 5px; margin-bottom: 18px; }
.question-topic { color: var(--accent); font-size: 10px; }
.question-toolbar strong { font-size: 12px; }
.question-numbers { display: grid; grid-template-columns: repeat(5,1fr); gap: 7px; }
.question-numbers button { aspect-ratio: 1; border: 1px solid var(--line); border-radius: 8px; color: var(--muted); background: var(--panel-2); font: 11px var(--mono); }
.question-numbers button:hover { color: var(--text); border-color: #424a54; }
.question-numbers button.active { border-color: var(--accent); color: var(--accent); background: var(--accent-wash); }
.question-focus { min-width: 0; padding: clamp(28px, 5vw, 64px); display: grid; align-content: center; justify-items: start; position: relative; background-image: radial-gradient(circle at 80% 25%, rgba(184,242,107,.045), transparent 16rem); }
.question-id { margin-bottom: 16px; color: var(--accent); font: 11px var(--mono); }
.question-focus h2 { max-width: 760px; margin: 0; color: var(--text); font-size: clamp(22px, 2.5vw, 35px); line-height: 1.5; letter-spacing: -.035em; word-break: keep-all; }
.question-focus h2 code { padding: 2px 7px; border-radius: 6px; color: var(--accent); background: var(--accent-wash); font: .78em var(--mono); }
.expected-output { margin-top: 24px; display: flex; align-items: center; gap: 12px; color: var(--text); font: 15px var(--mono); }
.expected-output span { color: var(--muted); font: 10px var(--sans); }
.expected-output code { padding: 7px 11px; border: 1px solid var(--line); border-radius: 8px; color: var(--accent); background: #0b0d0f; }
.question-actions { width: 100%; margin-top: 34px; display: flex; align-items: center; gap: 9px; }
.answer-button { margin: 0 auto; padding: 10px 14px; border: 1px solid var(--accent-deep); border-radius: 10px; color: var(--accent); background: var(--accent-wash); font-size: 11px; }
.focused-answer { width: 100%; margin-top: 18px; border: 1px solid var(--line); border-radius: 12px; overflow: hidden; background: #090b0d; }
.focused-answer > span { display: block; padding: 9px 14px; border-bottom: 1px solid var(--line-soft); color: var(--muted); font-size: 10px; }
.focused-answer pre { max-height: 150px; margin: 0; padding: 15px; overflow: auto; color: #ccd2d9; font: 11px/1.7 var(--mono); }
.focused-answer p { margin: 0; padding: 15px; color: var(--muted); font-size: 12px; }
.question-focus:has(.focused-answer) { padding-block: 22px; }
.question-focus:has(.focused-answer) .question-id { margin-bottom: 8px; }
.question-focus:has(.focused-answer) .expected-output { margin-top: 12px; }
.question-focus:has(.focused-answer) .question-actions { margin-top: 16px; }
.question-focus:has(.focused-answer) .focused-answer { margin-top: 10px; }

.guide-screen { grid-template-rows: auto auto auto auto; gap: 16px; }
.guide-principle { padding: 20px 26px; display: flex; align-items: center; justify-content: space-between; gap: 24px; border: 1px solid rgba(184,242,107,.28); border-radius: 16px; background: linear-gradient(110deg, var(--accent-wash), rgba(124,184,255,.04)); }
.guide-principle span { color: var(--accent); font: 10px var(--mono); }
.guide-principle strong { font-size: clamp(20px, 2.2vw, 30px); line-height: 1.25; text-align: right; letter-spacing: -.035em; }
.guide-flow { display: grid; grid-template-columns: 1fr auto 1fr auto 1fr; align-items: center; gap: 12px; }
.guide-flow > b { color: var(--faint); font-weight: 400; }
.guide-flow article { min-height: 135px; padding: 18px; border: 1px solid var(--line); border-radius: 15px; background: var(--panel); position: relative; }
.guide-flow article span { position: absolute; top: 14px; right: 14px; color: var(--faint); font: 10px var(--mono); }
.guide-flow article i { display: grid; width: 30px; height: 30px; place-items: center; margin-bottom: 13px; border-radius: 8px; color: var(--accent); background: var(--accent-wash); font-style: normal; }
.guide-flow h2 { margin: 0 0 5px; font-size: 16px; }
.guide-flow p { margin: 0; color: var(--muted); font-size: 11px; }
.prompt-card { display: grid; grid-template-columns: 170px 1fr auto; align-items: center; gap: 18px; padding: 16px 18px; border: 1px solid var(--line); border-radius: 15px; background: #0d0f12; }
.prompt-card > div span { color: var(--text); font-size: 12px; font-weight: 700; }
.prompt-card > div p { margin: 4px 0 0; color: var(--faint); font-size: 10px; }
.prompt-card pre { max-height: 68px; margin: 0; padding: 10px 12px; overflow: hidden; border: 1px solid var(--line-soft); border-radius: 9px; color: var(--muted); background: #090a0c; font: 9px/1.5 var(--mono); }
.guide-reminders { display: flex; justify-content: center; gap: 8px; }
.guide-reminders span { padding: 7px 10px; border: 1px solid var(--line-soft); border-radius: 999px; color: var(--muted); font-size: 10px; }

@media (max-width: 900px) {
  .app-shell { display: block; }
  .topbar { height: auto; min-height: 68px; grid-template-columns: auto 1fr; padding: 10px 18px; }
  .site-tabs { grid-column: 1 / -1; grid-row: 2; justify-self: stretch; justify-content: center; order: 3; }
  .site-tabs a { flex: 1; text-align: center; }
  .top-actions { grid-column: 2; grid-row: 1; }
  .concept-nav { justify-self: end; }
  .soundless-hint { display: none; }
  .brand span:last-child { display: none; }
  .concept-picker select { min-width: 0; width: min(44vw, 230px); }
  .concept-stage { padding: 20px 18px 42px; }
  .concept-screen { min-height: auto; grid-template-columns: 1fr; align-items: stretch; gap: 16px; }
  .lesson-copy { max-width: none; }
  .lesson-copy h1 { font-size: clamp(30px, 7vw, 44px); }
  .lab-body { height: auto; min-height: 500px; }
  .visual-area { padding: 36px 18px; overflow-x: auto; }
  .document-hero { padding-top: 26px; }
  .markdown-body { padding-top: 20px; }
  .resource-screen { min-height: auto; }
  .resource-header { align-items: start; }
  .category-rail { display: flex; overflow-x: auto; padding-bottom: 4px; scrollbar-width: none; }
  .category-rail button { flex: 0 0 104px; }
  .question-workspace { grid-template-columns: 170px 1fr; min-height: 520px; }
  .question-focus { padding: 34px; }
  .guide-flow article { min-height: 150px; }
  .prompt-card { grid-template-columns: 140px 1fr; }
  .prompt-card .action-button { grid-column: 1 / -1; }
}

@media (max-width: 560px) {
  .icon-button { width: 32px; }
  .concept-nav { gap: 5px; }
  .concept-picker select { font-size: 12px; }
  .memory-cell { width: 55px; min-height: 78px; }
  .memory-row { gap: 4px; }
  .type-grid { grid-template-columns: 1fr; }
  .heap { grid-template-columns: repeat(4, 1fr); }
  .controls { align-items: stretch; }
  .controls .segmented { overflow-x: auto; }
  .lesson-copy { align-items: start; flex-direction: column; gap: 10px; }
  .concept-rule { max-width: none; text-align: left; }
  .lab-hint { display: none; }
  .resource-header { flex-direction: column; gap: 9px; }
  .resource-header > p { text-align: left; }
  .question-workspace { display: block; min-height: 0; }
  .question-toolbar { border-right: 0; border-bottom: 1px solid var(--line); }
  .question-toolbar > div { margin-bottom: 12px; }
  .question-numbers { grid-template-columns: repeat(10,1fr); }
  .question-numbers button { aspect-ratio: auto; padding: 8px 0; }
  .question-focus { min-height: 420px; padding: 28px 20px; }
  .question-actions { flex-wrap: wrap; }
  .answer-button { order: -1; width: 100%; margin: 0; }
  .guide-principle { align-items: start; flex-direction: column; }
  .guide-principle strong { text-align: left; }
  .guide-flow { grid-template-columns: 1fr; }
  .guide-flow > b { rotate: 90deg; justify-self: center; }
  .prompt-card { grid-template-columns: 1fr; }
  .guide-reminders { align-items: stretch; flex-direction: column; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { scroll-behavior: auto !important; animation-duration: .01ms !important; transition-duration: .01ms !important; }
}