/* V4 original question-first workspace. References: research/v4-ui-references.md. */
:root{color-scheme:light;--bg:#f6f5f0;--surface:#fffefa;--surface-2:#eeeee7;--ink:#232f29;--muted:#657068;--line:#d9ded4;--accent:#146e59;--accent-hover:#0e5545;--accent-soft:#e9f3eb;--on-accent:#fff;--danger:#963e32;--danger-soft:#fff1eb;--danger-line:#dfbfb5;--pending:#78591c;--pending-soft:#faf3df;--pending-line:#ddceaa;--shadow:0 5px 24px #26382a05;font-family:"Microsoft YaHei UI","PingFang SC","Microsoft YaHei",sans-serif;font-size:15px;font-synthesis:none}
:root[data-theme=dark]{color-scheme:dark;--bg:#181d1b;--surface:#222925;--surface-2:#2b342e;--ink:#e9ece3;--muted:#b0b9af;--line:#414b43;--accent:#8ad6b8;--accent-hover:#b1e6cf;--accent-soft:#293f34;--on-accent:#15261c;--danger:#f1b3a6;--danger-soft:#3c2d29;--danger-line:#735046;--pending:#e7cb91;--pending-soft:#383429;--pending-line:#685d40;--shadow:none}
*{box-sizing:border-box}[hidden]{display:none!important}body{margin:0;background:var(--bg);color:var(--ink);line-height:1.7}button,input,select,textarea{font:inherit}button,.button{display:inline-flex;align-items:center;justify-content:center;gap:7px;min-height:44px;padding:8px 14px;background:var(--surface);border:1px solid var(--line);border-radius:7px;color:var(--ink);font-size:13px;font-weight:500;line-height:1.5;text-decoration:none;cursor:pointer}button:hover,.button:hover{background:var(--surface-2);border-color:var(--muted)}button:disabled{cursor:not-allowed;opacity:.46}.primary{background:var(--accent);border-color:var(--accent);color:var(--on-accent);font-weight:600}.primary:hover{background:var(--accent-hover);border-color:var(--accent-hover);color:var(--on-accent)}input,select,textarea{width:100%;max-width:100%;min-width:0;min-height:44px;padding:9px 12px;border:1px solid var(--line);border-radius:7px;background:var(--surface);color:var(--ink);line-height:1.5}input::placeholder,textarea::placeholder{color:var(--muted);opacity:1}input[type=radio],input[type=checkbox]{width:19px;height:19px;min-height:0;margin:0;accent-color:var(--accent);flex-shrink:0;cursor:pointer}label{font-size:12px;color:var(--muted)}label>input:not([type=checkbox]):not([type=radio]),label>select,label>textarea{display:block;margin-top:5px}h1,h2,h3,p{margin:0}h1{font-size:23px;font-weight:650;line-height:1.45;letter-spacing:.02em}h2{font-size:18px;font-weight:600;line-height:1.6}h3{font-size:13px;font-weight:600}a{color:var(--accent);text-underline-offset:4px;overflow-wrap:anywhere}small,.muted{font-size:12px;color:var(--muted)}.eyebrow{color:var(--muted);font-size:10px;letter-spacing:.16em;font-weight:600;margin-bottom:6px}:focus-visible{outline:3px solid var(--accent);outline-offset:4px}.skip{position:fixed;top:10px;left:10px;z-index:100;background:var(--surface);border:1px solid var(--accent);border-radius:6px;padding:10px 18px;transform:translateY(-200%)}.skip:focus{transform:none}
/* Shell: compact persistent course controls, quiet chapter rail. */
.topbar{display:flex;align-items:center;gap:24px;min-height:88px;padding:14px max(28px,calc((100vw - 1424px)/2));background:var(--surface);border-bottom:1px solid var(--line)}.brand{display:flex;align-items:center;gap:12px;margin-right:auto;min-width:0}.brand-mark{font-family:"STSong","SimSun",serif;display:grid;place-items:center;width:42px;height:42px;background:var(--accent);color:var(--on-accent);border-radius:7px;font-size:26px;line-height:1}.brand strong{font-size:17px;font-weight:650;letter-spacing:.04em}.brand small{display:block;margin-top:2px;font-size:10px;letter-spacing:.07em}.course-label{width:290px}.course-label select{font-size:13px;font-weight:600}.theme-label{width:112px;font-size:11px}.theme-label select{font-size:12px;padding:9px 8px}.layout{max-width:1424px;margin:auto;display:grid;grid-template-columns:238px minmax(0,1fr)}aside{padding:30px 20px;min-width:0;border-right:1px solid var(--line)}.chapter-panel-head{display:flex;align-items:center;justify-content:space-between}aside h2{font-size:15px;letter-spacing:.03em}#chapters{display:grid;gap:6px;margin-top:20px}#chapters button{width:100%;justify-content:flex-start;text-align:left;font-size:12px;font-weight:400;padding:10px 12px;border-color:transparent;background:transparent;white-space:normal;line-height:1.7;overflow-wrap:anywhere}#chapters button:hover{background:var(--surface-2)}#chapters button[aria-current=true]{background:var(--accent-soft);color:var(--accent);border-color:var(--line);font-weight:600}.chapter-name{flex:1;min-width:0}.chapter-count{color:var(--muted);font-size:10px;font-weight:400;white-space:nowrap;font-variant-numeric:tabular-nums}.side-note{font-size:11px;color:var(--muted);margin:30px 8px 0;padding-top:20px;border-top:1px solid var(--line);line-height:1.9}.side-note strong{font-size:11px;color:var(--ink);font-weight:500}.side-note p{margin-top:6px}#close-chapters,.mobile-chapter-bar{display:none}main{min-width:0;max-width:1186px;width:100%;padding:24px 36px 40px}
.mode-tabs{display:flex;gap:3px;border-bottom:1px solid var(--line);margin-bottom:22px}.mode-tabs button{position:relative;border:0;border-radius:0;background:transparent;color:var(--muted);padding:10px 18px;margin-bottom:-1px;font-size:13px;min-height:46px}.mode-tabs button:first-child{padding-left:0;padding-right:24px}.mode-tabs button[aria-pressed=true]{color:var(--accent);font-weight:650}.mode-tabs button[aria-pressed=true]::after{content:"";position:absolute;bottom:0;left:0;right:0;height:2px;background:var(--accent)}.intro{display:flex;align-items:center;justify-content:space-between;gap:16px;margin-bottom:20px}.intro .eyebrow{display:none}.intro .muted{margin-top:5px;font-size:11px}.toolbar{display:flex;align-items:center;gap:8px;flex-wrap:wrap}.intro .toolbar{flex-shrink:0}.intro .toolbar button,.intro .toolbar .button{background:transparent;font-size:11px;padding:8px 11px}.notice:empty{display:none}.notice{padding:12px 14px;background:var(--accent-soft);border:1px solid var(--line);border-radius:7px;font-size:13px;margin-bottom:16px;overflow-wrap:anywhere}.stats{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));margin-bottom:20px;gap:0}.stats>div{display:flex;align-items:baseline;justify-content:space-between;gap:8px;padding:0 20px;border-right:1px solid var(--line)}.stats>div:first-child{padding-left:0}.stats>div:last-child{padding-right:0;border:0}.stats span{font-size:11px;color:var(--muted);white-space:nowrap}.stats strong{font-size:22px;font-weight:550;letter-spacing:-.04em;font-variant-numeric:tabular-nums}.panel{padding:22px;border:1px solid var(--line);border-radius:12px;background:var(--surface);margin-bottom:18px;box-shadow:var(--shadow);min-width:0}
/* Filters stay secondary to the current question. */
.filters{padding:0;background:transparent;box-shadow:none;border:0;border-radius:0;margin-bottom:16px}.tabs{display:flex;gap:2px;width:fit-content;margin-bottom:8px}.tabs button{min-width:64px;min-height:44px;padding:7px 14px;border-color:transparent;background:transparent;color:var(--muted);font-size:12px}.tabs button:first-child{margin-left:-14px}.tabs button[aria-pressed=true]{color:var(--ink);font-weight:650;background:var(--surface-2)}.filter-grid{display:grid;grid-template-columns:minmax(0,1fr) auto;align-items:start;gap:12px}.search{font-size:0}.search input{margin-top:0!important;background:var(--surface);font-size:13px;min-height:44px}#advanced-filters{position:relative;border:0;margin:0;padding:0}summary{min-height:44px;cursor:pointer;font-weight:500;font-size:12px;line-height:1.8;list-style-position:inside;padding:10px 0}#advanced-filters>summary{padding:10px 12px;border:1px solid var(--line);border-radius:7px;white-space:nowrap;background:var(--surface);color:var(--ink)}#advanced-filters>summary span{display:none}#advanced-filters[open]{grid-column:1/-1}#advanced-filters[open]>summary{width:fit-content}.advanced-grid{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:12px;padding:14px 0 4px}.advanced-grid label{font-size:11px}.advanced-grid select{font-size:12px;padding-left:9px}.filter-bottom{display:flex;align-items:center;justify-content:space-between;gap:10px}#filter-count{font-size:11px}.text-button{border:0;background:transparent;font-size:11px;color:var(--muted);padding:8px 0}.text-button:hover{background:transparent;color:var(--accent);border-color:transparent}
/* The primary task uses a single paper surface, not a card dashboard. */
.question{padding:28px 32px 22px;box-shadow:var(--shadow);border-radius:12px}.question-top{display:flex;align-items:center;justify-content:space-between;gap:14px;margin-bottom:16px}#question-meta{display:flex;flex-wrap:wrap;gap:6px;min-width:0}.badge{font-size:10px;color:var(--muted);background:var(--surface-2);padding:3px 8px;border:1px solid transparent;border-radius:4px;line-height:1.6}.badge:first-child{color:var(--accent);background:var(--accent-soft);font-weight:600}#favorite{flex-shrink:0;font-size:11px;background:transparent;min-width:80px}#favorite[aria-pressed=true]{color:var(--accent);background:var(--accent-soft);border-color:var(--accent)}#stem{font-size:20px;font-weight:600;line-height:1.85;margin-bottom:22px;letter-spacing:.01em;white-space:pre-wrap;overflow-wrap:anywhere;color:var(--ink)}fieldset{margin:0;padding:0;border:0;min-width:0}legend{font-size:11px;color:var(--muted);padding:0;margin-bottom:10px}.choice{display:flex;align-items:flex-start;gap:14px;font-size:15px;color:var(--ink);border:1px solid var(--line);border-radius:7px;padding:13px 16px;margin-bottom:9px;line-height:1.75;cursor:pointer;min-height:54px;overflow-wrap:anywhere}.choice>input{margin-top:4px}.choice span{min-width:0;white-space:pre-wrap}.choice:hover{background:var(--surface-2);border-color:var(--muted)}.choice:has(input:checked){background:var(--accent-soft);border-color:var(--accent)}.choice:has(input:focus-visible){outline:2px solid var(--accent);outline-offset:3px}#written-label{display:block;font-size:12px}#written{font-size:15px;line-height:1.9;min-height:140px;resize:vertical;white-space:pre-wrap}.answer-actions{display:flex;align-items:center;gap:12px;flex-wrap:wrap;margin-top:18px}.instant-toggle{display:inline-flex;align-items:center;gap:8px;min-height:44px;color:var(--muted);font-size:12px;padding:8px 4px;cursor:pointer}#submit-answer{min-width:130px;order:-1}#answer-hint{flex-basis:100%;font-size:11px;line-height:1.8}#feedback{white-space:pre-wrap;padding:16px 18px;margin-top:24px;background:var(--surface-2);border:1px solid var(--line);border-radius:8px;font-size:13px;line-height:1.9;overflow-wrap:anywhere}#feedback[data-result=correct]{background:var(--accent-soft);color:var(--accent);border-color:var(--accent)}#feedback[data-result=wrong]{background:var(--danger-soft);color:var(--danger);border-color:var(--danger-line)}#feedback[data-result=pending]{background:var(--pending-soft);color:var(--pending);border-color:var(--pending-line)}#explanation{margin-top:14px;padding:6px 18px 14px;background:var(--surface-2);border:1px solid var(--line);border-radius:8px}#explanation summary{font-size:13px;color:var(--ink)}#explanation-content{white-space:pre-wrap;overflow-wrap:anywhere;font-size:14px;line-height:2;margin-top:5px}#self-assessment{font-size:12px;margin-top:16px}#self-assessment button{font-size:12px}.source{border-top:1px solid var(--line);padding-top:18px;margin-top:24px;color:var(--muted)}.source h3{font-size:11px;font-weight:500}.source p{font-size:10px;line-height:1.9;margin:6px 0;overflow-wrap:anywhere}.source button{font-size:11px;background:transparent;padding:8px 10px;margin-top:4px}#source-link{display:inline-flex;align-items:center;font-size:11px;min-height:44px;margin-right:12px}.question-footer{display:flex;align-items:center;justify-content:space-between;gap:10px;margin-top:20px;padding-top:18px;border-top:1px solid var(--line)}.question-footer button{font-size:12px;min-width:90px}.question-footer #next{color:var(--accent);border-color:var(--accent);background:var(--accent-soft)}#position{font-size:11px;color:var(--muted);font-variant-numeric:tabular-nums}.empty{padding:38px 24px;text-align:center}.empty p{color:var(--muted);margin:10px auto 20px;font-size:13px;max-width:500px}
#resources{padding:4px 0;border:0;box-shadow:none;background:transparent}#resources summary{font-size:11px;color:var(--muted)}#resource-content{font-size:12px;line-height:1.9;overflow-wrap:anywhere;padding:10px 0}#resource-content p{margin-bottom:12px}footer{font-size:10px;line-height:1.9;color:var(--muted);padding-top:6px}footer label{display:flex;align-items:center;gap:8px;min-height:44px;font-size:10px;width:fit-content;cursor:pointer}dialog{background:var(--surface);color:var(--ink);border:1px solid var(--line);border-radius:12px;max-width:min(1000px,96vw);width:94%;max-height:94dvh;padding:20px;overflow:auto}dialog::backdrop{background:#10241b99}dialog .toolbar{justify-content:space-between;margin-bottom:18px}dialog h2{font-size:14px;overflow-wrap:anywhere;flex:1}#original-image{display:block;width:100%;height:auto;margin-top:12px}#image-error{font-size:13px;padding:20px;background:var(--pending-soft);color:var(--pending)}
/* Exam remains isolated, answer-free until submission. */
body[data-mode=exam] .layout{display:block;max-width:1120px}body[data-mode=exam] main{max-width:none}body[data-mode=exam] .source,body[data-mode=exam] .mobile-chapter-bar{display:none}body[data-mode=exam] .intro .muted{display:none}body[data-mode=exam] .intro{margin-bottom:20px}.simulation-controls{padding:30px}.simulation-controls h2{font-size:26px;letter-spacing:.03em}.simulation-controls p{font-size:13px;line-height:1.9;max-width:730px;margin:10px 0 24px}.simulation-controls>label{display:block;font-size:12px;margin:20px 0}.simulation-controls select{font-size:14px}.simulation-controls .toolbar{margin-top:24px;align-items:end;gap:14px}.simulation-controls input{width:112px;font-variant-numeric:tabular-nums}#paper-info{padding:18px;background:var(--surface-2);border-radius:8px;font-size:13px;line-height:2}#exam-bar{padding:20px 22px}#exam-status{font-size:13px;font-weight:550}#timer{margin-left:auto;font-size:21px;font-weight:600;font-variant-numeric:tabular-nums;color:var(--accent);white-space:nowrap}#exam-summary{font-size:12px;line-height:1.9;color:var(--muted);margin:14px 0}#answer-card{display:grid;grid-template-columns:repeat(auto-fill,minmax(46px,1fr));gap:8px}#answer-card button{font-size:11px;min-width:0;min-height:44px;padding:6px 2px}#answer-card .answered{background:var(--accent-soft);color:var(--accent);border-color:var(--accent)}#answer-card button[aria-current=true]{outline:2px solid var(--accent);outline-offset:2px;font-weight:650}#leave-exam{margin-top:18px}#exam-self-score{padding:18px;background:var(--surface-2);border:1px solid var(--line);border-radius:8px;margin-top:18px}#exam-self-score input{max-width:140px;margin:8px 0}#self-score-note{display:block;font-size:12px;margin-top:8px;color:var(--muted)}
@media(min-width:768px) and (max-width:1100px){.layout{grid-template-columns:200px minmax(0,1fr)}main{padding:22px}aside{padding:26px 14px}.topbar{gap:16px;padding:14px 22px}.brand strong{font-size:15px}.brand small{font-size:9px}.course-label{width:240px}.intro{align-items:flex-start}.intro .toolbar{flex-direction:column}h1{font-size:20px}.stats>div{padding:0 10px;display:block}.stats strong{display:block;font-size:20px}.advanced-grid{grid-template-columns:repeat(2,minmax(0,1fr))}.question{padding:24px}}
@media(max-width:767px){.topbar{display:grid;grid-template-columns:minmax(0,1fr) 106px;padding:12px 16px;gap:10px 12px;min-height:0}.brand{grid-column:1/-1;margin:0;gap:9px}.brand-mark{width:30px;height:30px;font-size:20px;border-radius:5px}.brand strong{font-size:14px;letter-spacing:.03em}.brand small{display:none}.course-label,.theme-label{width:auto;font-size:0}.course-label select,.theme-label select{font-size:12px;min-height:44px;margin:0;padding:9px 8px}.layout{display:block}main{padding:12px 16px 24px}.mobile-chapter-bar{display:flex;align-items:center;gap:12px;margin-bottom:4px}#chapter-toggle{border:0;background:transparent;flex-shrink:0;font-size:11px;padding:8px 0;gap:12px;color:var(--ink)}#chapter-current{color:var(--muted);font-size:10px;white-space:nowrap;text-overflow:ellipsis;overflow:hidden;min-width:0}#chapter-panel{display:none;position:fixed;inset:0 auto 0 0;width:min(320px,85vw);height:100dvh;max-height:100dvh;overflow-y:auto;background:var(--surface);padding:24px 18px;z-index:51;border-right:1px solid var(--line)}body[data-drawer=open]{overflow:hidden}body[data-drawer=open] #chapter-panel{display:block}#close-chapters{display:inline-flex;font-size:12px}#chapter-panel .side-note{display:block}#chapters{margin-top:24px}#drawer-backdrop{position:fixed;inset:0;background:#0b151580;z-index:50}.mode-tabs{margin-bottom:12px;gap:0}.mode-tabs button{flex:1;font-size:12px;min-height:44px;padding:8px}.mode-tabs button:first-child{padding:8px}.intro{margin-bottom:12px}.intro>div:first-child{display:none}.intro .toolbar{gap:8px}.intro .toolbar button,.intro .toolbar .button{min-height:44px;font-size:10px;padding:8px 10px;border-color:transparent;color:var(--muted)}.stats{margin-bottom:10px}.stats>div{display:block;padding:0 10px;line-height:1.55}.stats span{font-size:9px;letter-spacing:-.03em}.stats strong{display:block;font-size:20px;margin-top:3px}.tabs{margin-bottom:5px;width:100%}.tabs button{min-width:0;flex:1;padding:7px 10px;font-size:11px}.tabs button:first-child{margin-left:0}.filter-grid{gap:8px;grid-template-columns:minmax(0,1fr) auto}.search input{font-size:12px;padding:9px 10px}#advanced-filters>summary{font-size:10px;padding:11px 9px}.advanced-grid{grid-template-columns:repeat(2,minmax(0,1fr));gap:10px}.advanced-grid select{font-size:11px;padding:9px 7px}.filters{margin-bottom:10px}.filter-bottom .muted{font-size:10px}.text-button{font-size:10px}.panel{margin-bottom:14px}.question{padding:18px 16px;border-radius:10px}.question-top{gap:8px;margin-bottom:12px;align-items:flex-start}.badge{font-size:9px;padding:3px 6px}#question-meta{gap:4px}#favorite{font-size:10px;min-width:68px;padding:8px}#stem{font-size:17px;line-height:1.9;margin-bottom:18px}.choice{font-size:14px;padding:13px 12px;gap:11px;margin-bottom:8px}.choice>input{margin-top:3px}.answer-actions{gap:10px}#submit-answer{min-width:120px;font-size:12px}.instant-toggle{font-size:11px}#answer-hint{font-size:10px}#feedback{font-size:12px;padding:14px}#explanation{padding:6px 14px 12px}#explanation-content{font-size:13px}.question-footer{gap:7px}.question-footer button{min-width:75px;font-size:11px;padding:8px 10px}#position{font-size:10px}.source p{font-size:10px}body[data-mode=exam] .intro{display:none}.simulation-controls{padding:22px 18px}.simulation-controls h2{font-size:22px}.simulation-controls p{font-size:12px}#paper-info{font-size:12px;padding:14px}#exam-bar{padding:16px}#exam-bar>.toolbar{gap:10px;justify-content:space-between}#exam-status{font-size:11px;flex-basis:100%}#timer{margin:0;font-size:19px}#exam-summary{font-size:11px}dialog{padding:16px}}
@media(max-width:767px){main{display:flex;flex-direction:column}.intro{order:9;margin-top:4px}footer{order:10}}
/* Scope is a single compact control, not another navigation row. */
.scope-row{display:flex;align-items:center;gap:14px;margin-bottom:6px}.scope-row>label{display:flex;align-items:center;gap:10px;font-size:11px;flex-shrink:0}.scope-row select{width:180px;margin:0;font-size:12px}.scope-row .muted{font-size:10px}.advanced-grid{grid-template-columns:repeat(3,minmax(0,1fr))}
@media(max-width:767px){.scope-row{display:block;margin:0 0 4px}.scope-row>label{font-size:0;gap:0}.scope-row select{width:100%;font-size:12px}.scope-row .muted{display:block;font-size:9px;line-height:1.7;margin-top:3px}.stats{margin-bottom:6px}#chapter-toggle{min-height:44px}.mobile-chapter-bar{margin-bottom:0}.question-top{margin-bottom:9px}#advanced-filters[open] .advanced-grid{grid-template-columns:repeat(2,minmax(0,1fr))}}
@media(max-width:767px){main{padding-top:6px}.mode-tabs{margin-bottom:6px}.question{padding-top:16px}.scope-row .muted{font-size:9px;margin-top:2px}}
/* One answer hierarchy: full answer first, result second, reasoning separate. */
#answer-summary{font-size:18px;font-weight:600;line-height:1.9;white-space:pre-wrap;overflow-wrap:anywhere;color:var(--accent);background:var(--accent-soft);border:1px solid var(--accent);border-radius:8px;padding:18px 20px;margin-top:22px}#answer-summary[data-status=pending]{color:var(--pending);background:var(--pending-soft);border-color:var(--pending-line)}#answer-summary+#feedback{margin-top:10px;font-size:12px;border-color:var(--line);background:transparent;color:var(--muted);padding:10px 0;border-width:0;border-radius:0}#reveal-answer{background:transparent;font-size:12px}#question-meta .badge{font-size:10px}#stem,.choice,#answer-summary,#explanation-content{font-family:inherit}
@media(max-width:767px){#answer-summary{font-size:16px;padding:15px 14px;line-height:1.9}#reveal-answer{font-size:11px}.instant-toggle{order:2}#answer-hint{order:3}}
@media(max-width:767px){.topbar{padding-top:8px;padding-bottom:8px}main{padding-top:4px}}
@media(min-width:768px){.mode-tabs{margin-bottom:16px}.intro{margin-bottom:16px}.stats{margin-bottom:16px}}
@media(prefers-reduced-motion:reduce){*,*::before,*::after{animation:none!important;transition:none!important;scroll-behavior:auto!important}}body[data-reduce-motion=true] *,body[data-reduce-motion=true] *::before,body[data-reduce-motion=true] *::after{animation:none!important;transition:none!important;scroll-behavior:auto!important}