/* REQ-0004 · Adapted from the approved typography research, at tool-page scale. */
:root, html[data-theme="light"] {
  --bg: #fff;
  --paper: #fff;
  --surface: #f5f5f7;
  --ink: #1d1d1f;
  --soft: #626268;
  --muted: #6e6e73;
  --line: #d6d6dc;
  --blue: #0066cc;
  --blue-light: #e5effb;
  --button: #0071e3;
  --button-hover: #0062c4;
  --focus: #0071e3;
  --diagram-ink: #333;
  --diagram-paper: #fff;
  --brand-orbit: #517a9c;
  --brand-orbit-end: #557896;
  --brand-core-top: #4c769b;
  --brand-core-bottom: #476887;
  --serif: "Lab Serif SC", "Noto Serif SC", "Songti SC", SimSun, serif;
  color-scheme: light;
}
html[data-theme="dark"] {
  --bg: #161617;
  --paper: #1d1d1f;
  --surface: #252527;
  --ink: #f5f5f7;
  --soft: #b8b8bd;
  --muted: #a1a1a8;
  --line: #46464c;
  --blue: #79baff;
  --blue-light: #203750;
  --button: #0071e3;
  --button-hover: #086acc;
  --focus: #79baff;
  --diagram-ink: #d7d7dc;
  --brand-orbit: #a4c9e9;
  --brand-orbit-end: #9ebadb;
  --brand-core-top: #4c7194;
  --brand-core-bottom: #46627f;
  color-scheme: dark;
}
*, *::before, *::after { box-sizing: border-box; }
html { scroll-padding-top: 24px; }
body { margin: 0; background: var(--bg); color: var(--ink); font-family: var(--serif); font-size: 17px; line-height: 1.75; font-synthesis: none; font-optical-sizing: auto; -webkit-font-smoothing: antialiased; }
button, input, select { font: inherit; color: inherit; }
button, summary { cursor: pointer; }
button, a, input, select { -webkit-tap-highlight-color: transparent; }
button { font-weight: 500; }
a { color: var(--blue); text-underline-offset: .2em; }
a:hover { text-decoration: underline; }
button:focus-visible, a:focus-visible, input:focus-visible, select:focus-visible, summary:focus-visible { outline: 3px solid var(--focus); outline-offset: 4px; }
button:disabled { opacity: .4; cursor: default; }
[hidden] { display: none !important; }
::selection { background: var(--blue-light); }
.shell { width: min(1320px, calc(100% - 80px)); margin-inline: auto; }
.skip-link { position: fixed; top: -80px; left: 20px; z-index: 10; background: var(--paper); padding: 12px; }
.skip-link:focus { top: 10px; }
.topbar { min-height: 76px; border-bottom: 1px solid var(--line); display: flex; justify-content: space-between; align-items: center; gap: 20px; padding-block: 12px; }
.brand { display: flex; align-items: center; gap: 10px; text-decoration: none; color: var(--ink); font-weight: 500; font-size: 15px; white-space: nowrap; }
.brand-atom { display: block; width: 80px; height: 80px; flex: none; overflow: visible; shape-rendering: geometricPrecision; }
.brand-orbits { fill: none; stroke: url(#lab-brand-orbits); stroke-width: 1.65; }
.brand-electrons { fill: var(--brand-orbit); stroke: var(--bg); stroke-width: .9; }
.brand-nucleus { fill: url(#lab-brand-core); }
.brand-atom text { fill: #fff; font-family: var(--serif); text-anchor: middle; }
.brand-atomic-number { font-size: 8.5px; font-weight: 500; }
.brand-element { font-size: 20px; font-weight: 600; letter-spacing: -.5px; }
.top-actions { display: flex; align-items: center; gap: 24px; }
.subject-label { color: var(--soft); font-size: 13px; }
.theme-switch { display: inline-flex; gap: 2px; padding: 3px; background: var(--surface); border-radius: 10px; }
.theme-switch button { border: 0; background: transparent; border-radius: 7px; font-size: 13px; min-height: 36px; padding: 5px 12px; color: var(--soft); line-height: 1.5; }
.theme-switch button[aria-pressed="true"] { background: var(--blue-light); color: var(--blue); }
.intro { display: flex; align-items: center; justify-content: space-between; padding: 36px 0 30px; gap: 32px; }
.eyebrow { font-size: 13px; font-weight: 500; color: var(--soft); margin: 0 0 10px; }
h1 { font-size: clamp(32px, 3.2vw, 44px); font-weight: 600; letter-spacing: -.025em; line-height: 1.3; margin: 0; text-wrap: balance; }
h1 span { display: inline-block; }
.intro-description { color: var(--soft); margin: 14px 0 0; font-size: 16px; line-height: 1.75; text-wrap: pretty; }
.catalog-stat { display: flex; gap: 28px; flex-shrink: 0; color: var(--soft); font-size: 12px; line-height: 1.6; }
.catalog-stat strong { display: block; font-size: 32px; font-weight: 600; line-height: 1.25; color: var(--ink); margin-bottom: 5px; font-variant-numeric: tabular-nums; }
.catalog-stat > span + span { padding-left: 28px; border-left: 1px solid var(--line); }
.mode-nav { display: flex; justify-content: space-between; align-items: center; gap: 24px; border-bottom: 1px solid var(--line); margin-bottom: 32px; }
.mode-options { display: flex; gap: 32px; }
.mode-options button { background: transparent; border: 0; border-bottom: 2px solid transparent; padding: 12px 2px 14px; min-height: 54px; font-size: 17px; color: var(--soft); margin-bottom: -1px; }
.mode-options button[aria-pressed="true"] { border-color: var(--blue); color: var(--blue); }
.learning-layout, .practice-layout { display: grid; grid-template-columns: 248px minmax(0, 1fr); gap: 40px; align-items: start; }
.catalog-panel, .practice-aside, .detail-panel, .paper-section, .knowledge-section, .illustration-section { min-width: 0; }
.catalog-panel { background: var(--surface); border-radius: 16px; padding: 20px 14px 16px; }
.catalog-head { display: flex; align-items: center; justify-content: space-between; margin: 0 6px 16px; }
.catalog-head h2 { margin: 0; font-size: 16px; font-weight: 600; }
.catalog-head > span { font-size: 12px; color: var(--soft); }
.scope-tabs { display: flex; gap: 4px; padding: 3px; background: var(--bg); border: 1px solid var(--line); border-radius: 10px; margin-bottom: 12px; }
.scope-tabs button { border: 0; background: transparent; flex: 1; padding: 7px 4px; min-height: 38px; border-radius: 7px; font-size: 13px; color: var(--soft); }
.scope-tabs button[aria-pressed="true"] { background: var(--blue-light); color: var(--blue); }
.search-wrap { position: relative; }
.search-wrap input { width: 100%; min-width: 0; background: var(--bg); border: 1px solid var(--line); border-radius: 10px; padding: 9px 30px 9px 11px; color: var(--ink); font-size: 14px; min-height: 44px; line-height: 1.5; }
.search-wrap input::placeholder { color: var(--soft); opacity: 1; }
.search-symbol { position: absolute; right: 12px; top: 8px; font-size: 18px; color: var(--soft); pointer-events: none; }
.category-filter { display: flex; flex-wrap: wrap; gap: 4px; margin: 12px 0; }
.category-filter button { border: 0; background: transparent; border-radius: 7px; min-height: 34px; padding: 5px 8px; font-size: 12px; color: var(--soft); }
.category-filter button[aria-pressed="true"] { background: var(--blue-light); color: var(--blue); }
.catalog-list { display: flex; flex-direction: column; gap: 4px; max-height: 540px; overflow: auto; padding: 3px 5px 5px 2px; scrollbar-width: thin; scrollbar-color: var(--line) transparent; }
.catalog-item { display: flex; align-items: center; text-align: left; border: 1px solid transparent; border-radius: 10px; background: transparent; padding: 9px 7px; gap: 10px; min-height: 64px; width: 100%; }
.catalog-item:hover { background: var(--bg); }
.catalog-item[aria-current="true"] { background: var(--blue-light); border-color: color-mix(in srgb, var(--blue) 28%, transparent); }
.catalog-mini { width: 37px; height: 40px; flex-shrink: 0; display: block; color: var(--diagram-ink); }
.catalog-item .item-copy { flex: 1; min-width: 0; }
.catalog-item strong { font-size: 14px; font-weight: 500; line-height: 1.65; display: block; overflow-wrap: anywhere; }
.catalog-item[aria-current="true"] strong { color: var(--blue); }
.catalog-item small { display: block; font-size: 11px; color: var(--soft); margin-top: 2px; font-weight: 400; }
.detail-heading { display: flex; justify-content: space-between; gap: 20px; align-items: center; margin-bottom: 12px; }
.detail-kicker { display: flex; flex-wrap: wrap; align-items: center; gap: 8px; color: var(--soft); font-size: 13px; font-variant-numeric: tabular-nums; }
.detail-heading h2 { font-size: 30px; line-height: 1.45; margin: 6px 0 0; font-weight: 600; letter-spacing: -.015em; overflow-wrap: anywhere; text-wrap: pretty; }
.secondary-button, .primary-button { border: 1px solid var(--line); border-radius: 10px; min-height: 44px; padding: 9px 15px; font-size: 14px; background: var(--paper); display: inline-flex; align-items: center; justify-content: center; gap: 7px; white-space: nowrap; line-height: 1.5; }
.secondary-button:hover { background: var(--surface); }
.secondary-button[aria-pressed="true"] { background: var(--blue-light); color: var(--blue); }
.detail-heading .secondary-button { color: var(--blue); flex-shrink: 0; }
.primary-button { border-color: var(--button); background: var(--button); color: #fff; }
.primary-button:hover { background: var(--button-hover); }
.detail-summary { font-size: 16px; color: var(--soft); margin: 0 0 24px; line-height: 1.8; text-wrap: pretty; }
.detail-body { display: grid; gap: 32px; align-items: start; }
.figure-card { background: #fff; border: 1px solid var(--line); border-radius: 16px; overflow: hidden; }
.figure-topline { display: flex; align-items: center; justify-content: space-between; flex-wrap: wrap; gap: 4px 16px; padding: 12px 18px; font-size: 12px; line-height: 1.8; color: var(--soft); background: var(--paper); border-bottom: 1px solid var(--line); }
.figure-topline > span > span { padding-inline: 4px; }
.figure-tools { display: flex; align-items: center; flex-wrap: wrap; gap: 16px; }
.text-button { border: 0; background: transparent; color: var(--blue); padding: 4px 0; min-height: 32px; font-size: 13px; line-height: 1.6; text-underline-offset: .2em; }
.text-button:hover { text-decoration: underline; }
.diagram-frame { position: relative; width: min(100%, 480px); aspect-ratio: 360 / 300; margin: 0 auto; }
.diagram-frame > svg, .question-diagram > svg { width: 100%; height: 100%; display: block; }
/* Exam line drawings stay black on white in both themes. */
.diagram-frame, .question-diagram, .welcome-drawing { --diagram-ink: #111; --diagram-paper: #fff; color: #111; background: #fff; }
.diagram-frame .hotspot { position: absolute; transform: translate(-50%, -50%); border: 1.5px solid #0066cc; border-radius: 50%; background: #fff; color: #0066cc; width: 30px; height: 30px; font: 500 13px var(--serif); box-shadow: 0 0 0 4px #ffffffc9; display: grid; place-items: center; padding: 0; z-index: 1; }
.diagram-frame .hotspot::after { content: ""; position: absolute; inset: -7px; border-radius: 50%; }
.diagram-frame .hotspot[aria-pressed="true"] { background: #0066cc; color: #fff; }
.hotspot-label { position: absolute; transform: translate(-50%, calc(-100% - 24px)); background: #0066cc; color: #fff; border-radius: 6px; padding: 4px 8px; font-size: 12px; font-weight: 500; width: max-content; max-width: min(136px, calc(100% / 3 - 10px)); white-space: normal; text-align: center; line-height: 1.5; z-index: 3; pointer-events: none; }
.hotspot-label::after { content: ""; position: absolute; top: 100%; left: calc(50% - 4px); border: 4px solid transparent; border-top-color: #0066cc; }
.hotspot-label.label-below { transform: translate(-50%, 24px); }
.hotspot-label.label-below::after { top: auto; bottom: 100%; border-top-color: transparent; border-bottom-color: #0066cc; }
.diagram-frame > svg.marker-leaders, .question-diagram > svg.marker-leaders { position: absolute; inset: 0; width: 100%; height: 100%; pointer-events: none; color: #6a8eaf; }
.figure-caption { padding: 16px 18px; border-top: 1px solid var(--line); color: var(--soft); min-height: 90px; display: flex; align-items: start; gap: 12px; background: var(--paper); }
.caption-number { width: 28px; height: 28px; display: grid; place-items: center; border: 1px solid var(--line); border-radius: 50%; font-size: 13px; flex-shrink: 0; color: var(--soft); margin-top: 1px; }
.figure-caption strong { font-weight: 500; color: var(--ink); display: block; font-size: 15px; line-height: 1.7; }
.figure-caption p { margin: 4px 0 0; font-size: 13px; line-height: 1.8; }
.part-chips { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 12px; }
.part-chips button { background: transparent; border: 1px solid var(--line); border-radius: 8px; padding: 8px 11px; font-size: 13px; line-height: 1.5; color: var(--soft); min-height: 40px; }
.part-chips button span { margin-right: 7px; color: var(--blue); font-variant-numeric: tabular-nums; }
.part-chips button[aria-pressed="true"] { background: var(--blue-light); color: var(--blue); border-color: transparent; }
.section-heading { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin-bottom: 14px; }
.section-heading h3 { font-size: 20px; font-weight: 600; margin: 0; line-height: 1.5; }
.facts { list-style: none; margin: 0; padding: 0; border-top: 1px solid var(--line); }
.fact-row { padding: 17px 0 19px; border-bottom: 1px solid var(--line); }
.fact-label { display: block; font-size: 13px; font-weight: 500; color: var(--soft); line-height: 1.7; margin-bottom: 6px; }
.fact-text { margin: 0; font-size: 17px; line-height: 1.9; overflow-wrap: anywhere; }
.key-term { color: inherit; font-weight: 600; background: transparent; }
.related-section { margin-top: 24px; }
.related-section h3 { font-size: 13px; font-weight: 500; color: var(--soft); margin: 0 0 10px; }
.related-links { display: flex; flex-wrap: wrap; gap: 6px 16px; }
.related-links button { border: 0; background: transparent; padding: 5px 0; font-size: 14px; color: var(--blue); min-height: 36px; text-align: left; }
.related-links button:hover { text-decoration: underline; text-underline-offset: .2em; }
.detail-bottom { display: flex; justify-content: flex-end; align-items: center; flex-wrap: wrap; gap: 12px; margin-top: 32px; border-top: 1px solid var(--line); padding-top: 20px; }
.nav-buttons { display: flex; gap: 8px; }
.empty-state { text-align: center; color: var(--soft); padding: 44px 16px; font-size: 15px; }
.empty-state p { margin: 8px 0; }
.loading { padding: 80px 20px; text-align: center; color: var(--soft); }
.practice-settings { padding: 22px 18px; background: var(--surface); border-radius: 16px; }
.practice-settings h2 { font-size: 18px; font-weight: 600; margin: 0 0 24px; }
.practice-settings fieldset { border: 0; padding: 0; margin: 0 0 22px; min-width: 0; }
.practice-settings legend { font-size: 14px; font-weight: 500; margin-bottom: 10px; padding: 0; }
.practice-settings select { width: 100%; border: 1px solid var(--line); border-radius: 9px; background: var(--bg); color: var(--ink); padding: 10px; min-height: 44px; font-size: 14px; line-height: 1.5; }
.radio-group { display: grid; gap: 8px; }
.radio-option { display: flex; align-items: center; gap: 10px; border: 1px solid var(--line); border-radius: 9px; padding: 11px 9px; font-size: 14px; cursor: pointer; position: relative; line-height: 1.65; }
.radio-option input { accent-color: var(--button); margin: 0; flex-shrink: 0; }
.radio-option:has(input:checked) { background: var(--blue-light); border-color: var(--blue); }
.radio-option strong { font-weight: 500; display: block; }
.radio-option small { display: block; font-size: 12px; color: var(--soft); margin-top: 3px; }
.quantity-options { display: flex; gap: 6px; }
.quantity-options label { flex: 1; text-align: center; cursor: pointer; }
.quantity-options input { position: absolute; opacity: 0; width: 1px; height: 1px; }
.quantity-options span { display: flex; align-items: center; justify-content: center; border: 1px solid var(--line); border-radius: 8px; padding: 8px 0; font-size: 13px; line-height: 1.5; min-height: 40px; }
.quantity-options input:checked + span { background: var(--blue-light); border-color: var(--blue); color: var(--blue); }
.quantity-options input:focus-visible + span { outline: 3px solid var(--focus); outline-offset: 3px; }
.practice-settings .primary-button { width: 100%; }
.pool-summary { font-size: 13px; color: var(--soft); margin: 0 0 16px; border-top: 1px solid var(--line); padding-top: 17px; }
.settings-note { font-size: 12px; line-height: 1.85; color: var(--soft); margin: 14px 0 0; }
.paper-toolbar { display: flex; align-items: center; justify-content: space-between; gap: 16px; margin-bottom: 18px; flex-wrap: wrap; }
.paper-toolbar h2 { font-size: 22px; font-weight: 600; margin: 0; }
.paper-toolbar .tools { display: flex; gap: 8px; flex-wrap: wrap; }
.paper-total { color: var(--soft); font-size: 14px; font-weight: 400; margin-left: 8px; }
.paper-meta { display: flex; align-items: center; justify-content: flex-end; flex-wrap: wrap; font-size: 13px; color: var(--soft); gap: 6px 16px; margin-bottom: 18px; }
.paper-progress { height: 3px; background: var(--line); border-radius: 3px; overflow: hidden; margin-bottom: 24px; }
.paper-progress span { display: block; height: 100%; background: var(--blue); }
.card-pager { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin: 0 0 16px; }
.card-pager > span { font-size: 14px; color: var(--soft); text-align: center; font-variant-numeric: tabular-nums; }
.card-stage { overflow: hidden; touch-action: pan-y; overscroll-behavior-x: contain; border-radius: 16px; }
.card-stage:focus-visible { outline: 3px solid var(--focus); outline-offset: 4px; }
.card-stage .question-card { margin-bottom: 0; transform: translateX(var(--card-drag-x, 0px)); }
.card-stage.is-dragging { cursor: grabbing; user-select: none; }
.question-card { background: var(--paper); border: 1px solid var(--line); border-radius: 16px; padding: 24px; margin-bottom: 20px; break-inside: avoid; }
.question-title { display: flex; align-items: center; flex-wrap: wrap; gap: 8px 12px; margin-bottom: 18px; }
.question-number { font-size: 22px; font-weight: 600; line-height: 1.5; color: var(--ink); font-variant-numeric: tabular-nums; }
.question-title h3 { font-size: 15px; margin: 0; font-weight: 500; }
.question-title .question-reveal { margin-left: auto; }
.question-content { display: grid; grid-template-columns: 200px minmax(0, 1fr); gap: 24px; align-items: start; }
.question-diagram { position: relative; aspect-ratio: 360 / 300; min-width: 0; border-radius: 10px; }
.question-marker { position: absolute; transform: translate(-50%, -50%); border: 1px solid #0066cc; border-radius: 50%; background: #fff; color: #0066cc; width: 23px; height: 23px; display: grid; place-items: center; font-size: 11px; font-weight: 500; }
.question-prompts { font-size: 17px; line-height: 2; min-width: 0; overflow-wrap: anywhere; }
.identify-line { margin: 0 0 14px; }
.part-answers { display: flex; flex-wrap: wrap; gap: 8px 16px; margin: 8px 0 16px; font-size: 15px; color: var(--soft); }
.question-facts { list-style: none; padding: 0; margin: 0; }
.question-facts li { margin: 12px 0; }
.blank { display: inline-flex; align-items: baseline; justify-content: center; min-width: 76px; min-height: 34px; vertical-align: baseline; max-width: 100%; padding: 1px 8px; margin: 0 3px; border: 0; border-bottom: 1px dashed var(--blue); border-radius: 4px 4px 0 0; background: var(--blue-light); color: var(--blue); font-size: inherit; font-weight: 400; line-height: 1.9; overflow-wrap: anywhere; text-align: center; }
.blank:hover { outline: 1px solid var(--blue); }
.blank-placeholder { font-family: var(--serif); font-size: 12px; font-weight: 500; }
.blank.revealed { font-weight: 500; border-bottom-style: solid; }
.mixed-facts { margin: 18px 0 2px; }
.mixed-facts summary { font-family: var(--serif); font-size: 14px; color: var(--blue); cursor: pointer; padding: 5px 0; min-height: 38px; }
.mixed-facts summary span { color: var(--soft); font-size: 12px; }
.mixed-facts[open] summary { margin-bottom: 10px; }
.practice-welcome { min-height: 490px; background: var(--surface); border-radius: 16px; display: flex; flex-direction: column; justify-content: center; align-items: center; text-align: center; padding: 40px 24px; }
.welcome-drawing { width: 130px; height: 110px; margin-bottom: 24px; border-radius: 12px; }
.practice-welcome h2 { font-size: 26px; font-weight: 600; line-height: 1.5; margin: 0 0 16px; text-wrap: balance; }
.practice-welcome p { font-size: 17px; color: var(--soft); line-height: 1.9; margin: 0; max-width: 350px; }
.practice-welcome ol { text-align: left; font-size: 15px; color: var(--soft); line-height: 2.3; padding-left: 22px; margin: 22px 0 0; }
.practice-view-bar { display: flex; flex-wrap: wrap; align-items: center; gap: 12px 24px; margin: -8px 0 28px; }
.practice-view-bar p { font-size: 13px; color: var(--soft); margin: 0; }
.practice-view-options { display: inline-flex; padding: 4px; gap: 4px; background: var(--surface); border-radius: 10px; }
.practice-view-options button { border: 0; border-radius: 7px; background: transparent; color: var(--soft); font-size: 15px; min-height: 44px; padding: 8px 20px; }
.practice-view-options button[aria-pressed="true"] { background: var(--blue-light); color: var(--blue); }
.worksheet, .worksheet-answer-key { background: var(--paper); border: 1px solid var(--line); padding: 32px; border-radius: 4px; }
.worksheet .paper-heading { text-align: center; padding-bottom: 24px; border-bottom: 1px solid var(--line); }
.worksheet .paper-heading h1 { font-size: 28px; }
.worksheet .paper-heading p { font-size: 13px; color: var(--soft); line-height: 2; margin: 16px 0 0; }
.worksheet .question-card { border: 0; border-bottom: 1px solid var(--line); border-radius: 0; padding: 28px 0; margin: 0; }
.worksheet .question-card:last-child { border-bottom: 0; padding-bottom: 0; }
.worksheet .question-content { grid-template-columns: 160px minmax(0, 1fr); gap: 20px; }
.worksheet .question-diagram { width: 100%; }
.worksheet .question-facts { margin-top: 18px; }
.worksheet-blank { display: inline-block; color: var(--ink); white-space: nowrap; margin: 0 4px; line-height: 1.8; }
.worksheet-answer-key { margin-top: 48px; scroll-margin-top: 24px; }
.worksheet-answer-key > h2 { font-size: 26px; font-weight: 600; text-align: center; margin: 0 0 24px; }
.worksheet-answer-key article { padding: 20px 0; border-top: 1px solid var(--line); break-inside: avoid; }
.worksheet-answer-key h3 { font-size: 17px; font-weight: 600; margin: 0 0 10px; }
.worksheet-answer-key p { font-size: 17px; line-height: 1.9; margin: 8px 0; overflow-wrap: anywhere; }
.worksheet-return { margin-top: 16px; }
.source-notes { margin-top: 48px; border-top: 1px solid var(--line); font-size: 13px; color: var(--soft); padding: 18px 0; }
.source-notes summary { cursor: pointer; width: fit-content; color: var(--soft); min-height: 32px; padding-block: 4px; }
.source-notes > div { max-width: 850px; line-height: 1.9; padding: 6px 0; overflow-wrap: anywhere; }
.source-notes p { margin: 12px 0; }
.footer { display: flex; align-items: center; justify-content: space-between; padding: 20px 0 32px; border-top: 1px solid var(--line); font-size: 12px; color: var(--soft); gap: 16px; flex-wrap: wrap; }
.footer a { text-decoration: none; color: var(--soft); }
.version { font-size: 11px; margin-left: 8px; }
.toast { position: fixed; bottom: 24px; left: 50%; transform: translateX(-50%); padding: 12px 20px; border: 1px solid var(--line); border-radius: 12px; background: var(--paper); box-shadow: 0 4px 20px #0002; color: var(--ink); font-size: 14px; z-index: 20; max-width: calc(100% - 32px); text-align: center; }
.print-only { display: none; }
@media (min-width: 1180px) {
  .detail-body { grid-template-columns: minmax(0, 1.08fr) minmax(0, 1fr); gap: 32px; }
  .catalog-panel, .practice-aside { position: sticky; top: 24px; }
}
@media (max-width: 1179px) {
  .shell { width: calc(100% - 64px); }
  .learning-layout, .practice-layout { grid-template-columns: 224px minmax(0, 1fr); gap: 28px; }
  .catalog-panel { padding-inline: 12px; }
  .catalog-stat { gap: 20px; }
  .catalog-stat > span + span { padding-left: 20px; }
  .detail-heading h2 { font-size: 28px; }
  .question-content { grid-template-columns: 1fr; gap: 20px; }
  .question-diagram { width: min(100%, 260px); margin-inline: auto; }
  .worksheet .question-content { grid-template-columns: minmax(0, 1fr); }
  .worksheet .question-diagram { width: min(100%, 220px); }
}
@media (max-width: 850px) {
  .shell { width: calc(100% - 40px); }
  .learning-layout, .practice-layout { grid-template-columns: 200px minmax(0, 1fr); gap: 24px; }
  .subject-label { display: none; }
  .catalog-stat { display: none; }
  .catalog-panel { padding-inline: 10px; }
  .catalog-item { gap: 6px; padding-inline: 5px; }
  .catalog-mini { width: 29px; height: 36px; }
  .catalog-item strong { font-size: 13px; }
  .scope-tabs button { font-size: 12px; }
  .search-wrap input { font-size: 13px; }
  .category-filter button { padding-inline: 6px; }
  .detail-heading { flex-wrap: wrap; gap: 12px; }
  .detail-summary { font-size: 15px; }
  .practice-settings { padding-inline: 14px; }
}
@media (max-width: 720px) {
  .topbar { min-height: 72px; gap: 12px; flex-wrap: wrap; }
  .brand { font-size: 13px; gap: 8px; }
  .brand-atom { width: 72px; height: 72px; }
  .top-actions { margin-left: auto; }
  .theme-switch button { font-size: 12px; padding-inline: 9px; min-height: 34px; }
  .intro { padding: 30px 0 24px; }
  .intro-description { font-size: 15px; max-width: 340px; margin-top: 12px; }
  .eyebrow { font-size: 12px; margin-bottom: 9px; }
  .mode-nav { margin-bottom: 24px; gap: 16px; }
  .mode-options { gap: 28px; }
  .mode-options button { font-size: 16px; }
  .learning-layout, .practice-layout { grid-template-columns: minmax(0, 1fr); gap: 28px; }
  .catalog-panel { border-radius: 14px; padding: 16px 12px 10px; position: static; }
  .catalog-head { margin: 0 2px 12px; }
  .catalog-head h2 { font-size: 15px; }
  .catalog-toolbar { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; }
  .scope-tabs { margin: 0; }
  .scope-tabs button { font-size: 13px; }
  .search-wrap input { font-size: 16px; padding-left: 10px; }
  .category-filter { margin: 10px 0 6px; flex-wrap: nowrap; overflow: auto; padding: 1px 0 4px; scrollbar-width: none; }
  .category-filter button { white-space: nowrap; flex-shrink: 0; padding-inline: 8px; min-height: 36px; }
  .catalog-list { flex-direction: row; gap: 8px; overflow-x: auto; overflow-y: hidden; max-height: none; padding: 3px 2px 7px; scroll-padding-inline: 2px; }
  .catalog-item { width: 114px; min-width: 114px; max-width: 150px; flex-shrink: 0; flex-direction: column; gap: 5px; align-items: center; text-align: center; border-color: var(--line); background: var(--bg); padding: 9px 8px; min-height: 94px; }
  .catalog-item .catalog-mini { width: 42px; height: 38px; }
  .catalog-item strong { font-size: 12px; line-height: 1.65; }
  .catalog-item small { display: none; }
  .detail-heading { flex-wrap: nowrap; margin-bottom: 12px; gap: 12px; }
  .detail-heading h2 { font-size: 28px; }
  .detail-kicker { font-size: 12px; gap: 6px; }
  .detail-heading .secondary-button { font-size: 13px; padding-inline: 11px; }
  .detail-summary { font-size: 16px; margin-bottom: 20px; }
  .detail-body { gap: 28px; }
  .figure-card { border-radius: 14px; }
  .figure-topline { padding: 10px 14px; font-size: 11px; gap: 0 12px; }
  .figure-tools { gap: 14px; }
  .figure-tools .text-button { font-size: 12px; }
  .diagram-frame .hotspot { width: 28px; height: 28px; font-size: 12px; }
  .hotspot-label { font-size: 11px; max-width: min(94px, calc(100% / 3 - 10px)); }
  .figure-caption { padding: 15px 14px; min-height: 92px; }
  .figure-caption p { font-size: 13px; }
  .part-chips { gap: 8px; }
  .part-chips button { font-size: 12px; }
  .section-heading h3 { font-size: 20px; }
  .fact-row { padding-block: 16px 18px; }
  .fact-text { font-size: 17px; }
  .detail-bottom { margin-top: 28px; }
  .detail-bottom .nav-buttons { margin-left: auto; }
  .practice-settings { padding: 20px 16px; }
  .practice-settings select { font-size: 16px; }
  .practice-form-grid { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); gap: 0 16px; }
  .practice-settings .type-field { grid-column: 1 / -1; }
  .radio-group { grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 7px; }
  .radio-option { padding: 12px 7px; gap: 6px; font-size: 13px; }
  .radio-option small { display: none; }
  .quantity-options span { min-height: 44px; font-size: 14px; }
  .practice-welcome { min-height: 340px; padding: 28px 20px; }
  .practice-welcome h2 { font-size: 25px; }
  .paper-toolbar { gap: 12px; }
  .paper-toolbar h2 { font-size: 20px; }
  .paper-toolbar .secondary-button { font-size: 13px; padding-inline: 12px; }
  .card-pager { gap: 8px; }
  .card-pager .secondary-button { font-size: 13px; padding-inline: 10px; }
  .card-pager > span { font-size: 12px; }
  .paper-meta { font-size: 12px; }
  .question-card { padding: 20px 16px; border-radius: 14px; }
  .question-title { gap: 8px; margin-bottom: 12px; }
  .question-title h3 { font-size: 14px; }
  .question-title .text-button { font-size: 12px; }
  .question-diagram { width: min(100%, 240px); }
  .question-content { gap: 16px; }
  .question-prompts { font-size: 17px; }
  .worksheet, .worksheet-answer-key { padding: 24px 16px; }
  .worksheet .paper-heading h1 { font-size: 25px; }
  .worksheet .paper-heading p { text-align: left; }
  .worksheet-answer-key { margin-top: 32px; }
  .source-notes { margin-top: 36px; }
}
@media (max-width: 359px) {
  .topbar { flex-wrap: wrap; gap: 12px; padding-block: 16px; }
  .top-actions { margin-left: auto; }
  h1 { font-size: 30px; }
  .mode-nav { gap: 12px; }
  .mode-nav > span { max-width: 140px; }
  .catalog-toolbar { grid-template-columns: minmax(0, 1fr); }
  .catalog-item { min-width: 106px; width: 106px; }
  .detail-heading { align-items: start; flex-wrap: wrap; }
  .detail-heading h2 { font-size: 26px; }
  .detail-heading .secondary-button { margin-left: auto; }
  .figure-topline { padding-inline: 12px; }
  .radio-group { grid-template-columns: 1fr; }
  .radio-option { font-size: 14px; padding: 10px; }
  .radio-option small { display: block; }
  .question-title .question-reveal { margin-left: 0; }
  .question-card { padding-inline: 14px; }
  .part-answers { font-size: 14px; }
}
@media (pointer: coarse) {
  .theme-switch button, .scope-tabs button, .category-filter button, .text-button, .part-chips button, .related-links button, .mixed-facts summary, .source-notes summary { min-height: 44px; }
  .blank { min-height: 40px; }
}
@media (prefers-reduced-motion: no-preference) { html { scroll-behavior: smooth; } .paper-progress span { transition: width .2s; } }
@media (prefers-reduced-motion: no-preference) {
  .card-stage[data-direction="next"]:not(.is-dragging) .question-card { animation: card-next .18s ease-out; }
  .card-stage[data-direction="previous"]:not(.is-dragging) .question-card { animation: card-previous .18s ease-out; }
  @keyframes card-next { from { opacity: .65; transform: translateX(36px); } to { opacity: 1; transform: translateX(0); } }
  @keyframes card-previous { from { opacity: .65; transform: translateX(-36px); } to { opacity: 1; transform: translateX(0); } }
}
@media print {
  @page { size: A4; margin: 16mm; }
  html, body { background: #fff !important; color: #222 !important; font-size: 11px; }
  .shell { width: 100%; }
  .topbar, .intro, .mode-nav, .practice-aside, .practice-view-bar, .paper-toolbar, .paper-meta, .paper-progress, .source-notes, .footer, .toast, .question-reveal, .paper-end, .skip-link, .worksheet-return { display: none !important; }
  .practice-layout { display: block; }
  .card-pager, .card-stage { display: none !important; }
  .card-print-questions.print-only { display: block; }
  .paper-heading.print-only { display: block; text-align: center; border-bottom: 1px solid #333; padding-bottom: 14px; margin-bottom: 18px; }
  .paper-heading h1 { font-size: 24px; color: #222; }
  .paper-heading p { font-size: 11px; }
  .question-card { background: #fff; color: #222; border: 0; border-bottom: 1px solid #ccc; border-radius: 0; padding: 14px 0; margin: 0; box-shadow: none; break-inside: avoid; }
  .question-content { grid-template-columns: 160px minmax(0, 1fr); gap: 15px; }
  .question-diagram { width: 160px; }
  .question-title h3, .question-number { color: #222; }
  .blank { background: transparent !important; border-radius: 0; border-bottom: 1px solid #555 !important; color: transparent !important; min-width: 80px; min-height: 23px; padding: 0 6px; }
  .blank > span { visibility: hidden !important; }
  .question-marker { color: #222; border-color: #333; background: #fff; }
  .question-prompts { font-size: 11px; }
  .print-answer-key { display: block; break-before: page; font-size: 11px; }
  .print-answer-key h2 { text-align: center; font-size: 22px; font-weight: 600; }
  .print-answer-key article { break-inside: avoid; border-bottom: 1px solid #ccc; padding: 8px 0; }
  .print-answer-key h3 { font-size: 12px; margin: 0 0 4px; }
  .print-answer-key p { margin: 4px 0; line-height: 1.8; }
  .print-answer-key .key-term { color: #222; }
  .question-facts li { margin: 6px 0; }
  .figure-card, .knowledge-section { break-inside: avoid; }
  .detail-body { display: block; }
  .mixed-facts > summary { display: none !important; }
  .marker-leaders { color: #333 !important; }
  .worksheet, .worksheet-answer-key { padding: 0; margin: 0; border: 0; background: #fff; }
  .worksheet .paper-heading { border-color: #333; padding-bottom: 14px; margin-bottom: 18px; }
  .worksheet .paper-heading h1 { font-size: 24px; }
  .worksheet .paper-heading p { font-size: 11px; color: #222; text-align: center; }
  .worksheet .question-card { border-bottom: 1px solid #ccc; padding: 14px 0; }
  .worksheet .question-content { grid-template-columns: 140px minmax(0, 1fr); gap: 15px; }
  .worksheet .question-diagram { width: 140px; }
  .worksheet .question-facts { margin-top: 10px; }
  .worksheet-blank { color: #222; }
  .part-answers { color: #222; }
  .worksheet-answer-key { break-before: page; page-break-before: always; }
  .worksheet-answer-key > h2 { font-size: 22px; margin-bottom: 18px; }
  .worksheet-answer-key article { padding: 8px 0; border-color: #ccc; }
  .worksheet-answer-key h3 { font-size: 12px; margin-bottom: 4px; }
  .worksheet-answer-key p { font-size: 11px; margin: 4px 0; }
}