@font-face{font-family:MathText;src:local("Georgia")}*{box-sizing:border-box} :root{--bg:#f5f3ed;--paper:#fcfbf7;--ink:#303a35;--muted:#747a73;--line:#dedfd5;--green:#435d4c;--wash:#e9ede3;--rust:#a26645;--blue:#607993;--red:#a24d40}body{margin:0;background:var(--bg);color:var(--ink);font:14px/1.75 -apple-system,BlinkMacSystemFont,"Segoe UI","Microsoft YaHei",sans-serif}button,input,select,textarea{font:inherit}button,a,input,select,textarea{-webkit-tap-highlight-color:transparent}button{cursor:pointer;border:1px solid var(--line);background:transparent;color:var(--ink);padding:8px 15px;border-radius:6px;min-height:42px}button:hover{background:var(--wash)}button:disabled{opacity:.5;cursor:default}a{color:var(--green);text-decoration:none}a:hover{text-decoration:underline}input,select,textarea{background:var(--paper);color:var(--ink);border:1px solid var(--line);border-radius:5px;padding:10px 12px;min-width:0;max-width:100%}input:focus,select:focus,textarea:focus{outline:2px solid #819b85;outline-offset:1px}button:focus-visible,a:focus-visible,summary:focus-visible{outline:2px solid var(--green);outline-offset:4px}input[type=checkbox],input[type=radio]{accent-color:var(--green)}textarea{width:100%;resize:vertical;min-height:110px}h1,h2,h3,p{margin:0}h1{font-family:Georgia,"Songti SC","SimSun",serif;font-weight:400;font-size:38px;line-height:1.5;letter-spacing:1px}h2{font-size:20px;font-weight:500;line-height:1.6}h3{font-size:15px;font-weight:600}small,.muted,.tiny{color:var(--muted)}small{font-size:12px}.tiny{font-size:11px;letter-spacing:1px}.rail{width:238px;position:fixed;inset:0 auto 0 0;padding:38px 25px 25px;border-right:1px solid var(--line);display:flex;flex-direction:column;background:#eeeee5;z-index:20}.brand{display:flex;gap:13px;align-items:center;color:var(--ink);font-size:11px;white-space:nowrap}.brand:hover{text-decoration:none}.brand small{display:block;font-size:8px;letter-spacing:1.7px;margin-top:5px}.seal{font:42px/1.3 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.meta{font-size:10px;color:var(--muted);display:flex;gap:10px;margin-bottom:5px;flex-wrap:wrap}.question-row .preview{font-size:13px;line-height:1.9;max-height:3.8em;overflow:hidden}.question-row .arrow{color:var(--muted)}.list-bar{display:flex;justify-content:space-between;align-items:center;font-size:11px;color:var(--muted);gap:15px;margin:10px 0 17px}.link-button{border:0;padding:5px 0;min-height:34px;color:var(--green);font-size:12px}.primary{background:var(--green);color:#fff;border-color:var(--green)}.primary:hover{background:#334d3e}.secondary{background:var(--paper)}.button-row{display:flex;gap:10px;align-items:center;flex-wrap:wrap}.pager{display:flex;gap:15px;align-items:center;justify-content:center;margin-top:24px;font-size:12px}.empty{padding:44px 12px;text-align:center;color:var(--muted);border-top:1px solid var(--line)}.exercise{max-width:850px;margin:auto;padding:26px 0 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var(--green);border-radius:0}#toast{position:fixed;bottom:30px;left:50%;transform:translateX(-50%);background:var(--ink);color:white;padding:12px 22px;border-radius:7px;max-width:calc(100% - 30px);z-index:60;font-size:12px}#save-state.warning{color:var(--red)}.skip{position:fixed;top:-80px;left:20px;z-index:100;background:white;padding:10px}.skip:focus{top:10px}.batch-note{font-size:11px;color:var(--muted);margin:15px 0}.inline-status{font-size:11px;color:var(--muted)}
@media(min-width:1400px){.shell{padding:0 75px}.workspace{grid-template-columns:240px minmax(0,1fr);gap:45px}.intro{padding-top:50px;padding-bottom:42px}}
@media(max-width:1100px){.rail{width:198px;padding:30px 18px}.shell{margin-left:198px;padding:0 28px}.brand{gap:10px;font-size:10px}.workspace{grid-template-columns:170px minmax(0,1fr);gap:20px}.tools-layout,.error-tool{grid-template-columns:210px minmax(0,1fr);gap:20px}.orbit{width:130px}.q-paper{padding:26px}}
@media(max-width:760px){body{font-size:13px}.rail{inset:auto 0 0;width:100%;height:calc(64px + env(safe-area-inset-bottom));padding:0 12px env(safe-area-inset-bottom);border:0;border-top:1px solid var(--line);background:#f5f3edf5}.brand,.rail-bottom{display:none}.rail nav{display:flex;justify-content:space-around;margin:0;gap:4px;height:64px}.rail nav a{padding:8px 12px;display:flex;flex-direction:column;gap:2px;font-size:11px;letter-spacing:0;justify-content:center;min-width:64px}.rail nav a span{font-size:10px}.shell{margin-left:0;padding:0 20px 70px}.topbar{height:62px;font-size:10px}.topbar #save-state{cursor:pointer}h1{font-size:29px}.intro{padding:30px 0 25px;gap:10px}.intro p{font-size:11px;max-width:250px}.eyebrow{font-size:9px}.orbit{width:86px;height:95px}.stats{gap:15px;margin-top:18px;font-size:10px}.stats b{font-size:19px}.workspace{display:block;padding-top:16px}.topics{flex-direction:row;overflow:auto;margin:0 -20px 18px;padding:0 20px 8px;gap:6px}.topic{white-space:nowrap;min-height:40px;padding:8px 12px;border:1px solid var(--line);border-radius:20px;gap:10px}.topic-kicker,.sidebar-note{display:none}.filters{gap:6px}.filters input,.filters select{min-height:42px;padding:8px;font-size:12px}.filters select{max-width:calc(50% - 4px);flex:1}.filters .search{width:100%;flex-basis:100%}.filters input{min-width:0}.list-bar{font-size:10px}.question-row{padding:15px 0;gap:7px;grid-template-columns:19px minmax(0,1fr) 14px}.question-row .preview{font-size:12px}.question-row .meta{font-size:9px;gap:8px}.exercise{padding:18px 0}.exercise-top{margin-bottom:18px;font-size:11px}.q-paper{padding:22px 18px;border-radius:6px}.q-prompt{font-size:16px;margin:25px 0;line-height:2.2}.answer-row{flex-wrap:wrap}.answer-row input{width:100%;flex-basis:100%;font-size:16px}.answer-row button{flex:1}.flags{gap:6px}.flag{padding:6px 9px;font-size:10px;min-height:40px}.option{padding:11px;font-size:13px}.history-row{flex-wrap:wrap;gap:3px}.tools-layout{display:flex;flex-direction:column;gap:20px}.tool-params{grid-template-columns:1fr 1fr;gap:12px}.tool-params>.field:first-child,.tool-params>details,.tool-params>.button-row{grid-column:1/-1}.tool-params input{font-size:16px;width:100%}.range-fields{grid-column:1/-1}.plot{height:285px}.plot-toolbar{padding:12px;gap:10px;font-size:10px}.plot-readout{padding:10px 12px;font-size:10px}.results{grid-template-columns:repeat(3,minmax(0,1fr));margin-top:14px}.result{padding:12px 7px}.result b{font-size:16px}.result small{font-size:9px}.error-tool{display:block;margin-top:30px}.error-tool>div:first-child{margin-bottom:20px}.error-inputs input{font-size:16px;width:100%}.formula-display{font-size:14px;padding:22px 0}.formula-head h3{font-size:14px}.formula-item{padding:20px 0}.formula-notes{font-size:12px}.record-tabs{gap:6px}.record-tabs button{padding:7px 11px;font-size:11px}footer{font-size:9px;gap:7px;flex-wrap:wrap}.footer-version{width:100%;margin:0}dialog{padding:25px}#toast{bottom:85px;white-space:normal;width:max-content}.katex-display>.katex{white-space:nowrap}.formula-display{overflow-x:auto}}
@media(prefers-reduced-motion:no-preference){button,a{transition:background .15s,color .15s}}
/* Quiet blue-black-violet workspace. The backdrop never animates or intercepts input. */
#save-state{font:inherit;padding:3px 0;min-height:32px;color:inherit;border:0;text-align:right;max-width:60%}#save-state:hover{background:transparent;color:var(--ink)}
:root{color-scheme:dark;--bg:#0e1221;--paper:#171c30;--ink:#dcdfee;--muted:#929bb4;--line:#30364d;--green:#bbb5e6;--wash:#252b45;--rust:#afa1d4;--blue:#8faecc;--red:#e3a59e}
body{background:#0e1221 url('atmosphere.svg') center top/cover fixed no-repeat;letter-spacing:.1px}
.rail{background:#101527c9;border-right-color:#34374b90}.rail nav a.active{background:#30334e;color:#e3dcff}.rail nav a:hover{background:#232a41}.account-button{color:#c1c5da}.dot{background:#9d94c7}.topbar{border-color:#3a3d524d}.shell{max-width:1640px}.intro h1{color:#e0e2f2;letter-spacing:2px;font-size:34px}.eyebrow{color:#a69ac9}.intro p{color:#a0a7bf}.stats b{color:#c6c3ed}.stats{gap:30px}
.workspace{background:#12192bd9;border:1px solid #34394f8c;border-radius:10px;padding:23px;gap:24px;box-shadow:0 15px 60px #070a1620}.topic.active{background:#2b304d;color:#d6cefa}.question-row:hover{background:#20263c}.question-row .mark{color:#66718c}.question-row .mark.done{color:#b9b0e3}.question-row .meta{color:#959db6}.question-row .preview{color:#d2d8ec}.primary{background:#9c97c8;color:#111629;border-color:#aca5db;font-weight:500}.primary:hover{background:#b5aede}.secondary{background:#22283f}button:hover{background:#2a304a}.q-paper{background:linear-gradient(145deg,#1d2337f5,#151b2ff8);border-color:#424760;border-top-color:#6c6388;box-shadow:0 18px 70px #05081430}.q-prompt{color:#e3e6f4}.feedback{background:#2b304b;color:#d3d0ed}.feedback.error{background:#3c2938;color:#e4b1ba}.option:has(input:checked){background:#30334e;border-color:#9b91c4}.flag[aria-pressed=true]{background:#383650;border-color:#9588bc}.error-result{background:#252d45}.record-tabs button.active{background:#33334f;border-color:#8a80ab}.plot-wrap{background:#151b2ef2;border-color:#3a415b}.result{background:#151b2eb0}.plot-readout{color:#a3acc7}.formula-item{border-color:#343b53}.formula-display{color:#dddff5}.formula-head h3{font-weight:500}.formula-notes strong{color:#d9dcef}.error-tool{border-color:#343b53}.empty{color:#9ba4bf}.option{border-color:#3b435e}.details summary{color:#a0a9c4}input,select,textarea{background:#11182b;border-color:#3e4763;color:#dfe3f3}input::placeholder,textarea::placeholder{color:#7f8aa6}input:focus,select:focus,textarea:focus{outline-color:#a89cd3}button:focus-visible,a:focus-visible,summary:focus-visible{outline-color:#b4a6df}input[type=checkbox],input[type=radio]{accent-color:#a89dd2}#toast{background:#d4d0eb;color:#171b2b;box-shadow:0 8px 40px #0005}dialog{background:#192036;border-color:#444c69}dialog::backdrop{background:#030712b5}.skip{background:#1e2540}.difficulty-tabs{display:flex;gap:9px;align-items:center;margin:0 0 19px}.difficulty-tabs button{padding:9px 18px;font-size:13px;letter-spacing:1px;background:#141a2dcc}.difficulty-tabs button.active{background:#36334f;border-color:#8e80b2;color:#e5dcff}.difficulty-tabs button small{font-size:10px;padding-left:12px;letter-spacing:0;color:#a0a4be}.difficulty-tabs>span{font-size:10px;color:#8d97b1;margin-left:auto}.record-item pre{font-family:inherit}.rail nav a{font-size:13px}.stats{font-size:11px}.footer-version{color:#77839f}.brand small{color:#8991b1}footer{color:#8991ab}.exercise{padding-top:30px}.answer-row input{letter-spacing:.5px}
@media(min-width:1500px){.exercise{max-width:900px}.q-paper{padding:40px 45px}.shell{padding-left:65px;padding-right:65px}}
@media(max-width:1100px){.workspace{padding:17px;gap:18px}}
@media(max-width:760px){body{background-size:auto 100vh;background-position:65% 0}.rail{background:#11172af5;border-top-color:#384059}.shell{padding-left:18px;padding-right:18px}.intro h1{font-size:27px}.intro{padding:26px 0 23px}.workspace{padding:16px 13px;border-radius:8px}.topics{margin:0 -13px 18px;padding:0 13px 10px}.difficulty-tabs{gap:7px;flex-wrap:wrap;margin-bottom:15px}.difficulty-tabs button{padding:8px 13px;font-size:12px;flex:1}.difficulty-tabs button small{padding-left:8px;font-size:9px}.difficulty-tabs>span{display:block;width:100%;margin:0;font-size:9px}.q-paper{padding:24px 19px}.q-prompt{font-size:16px}.rail nav a{font-size:11px}.exercise-top{font-size:10px}.q-meta{font-size:10px}.topbar{font-size:10px}.flag{font-size:10px}dialog{background:#192036}.stats{gap:20px}.formula-display{padding-right:5px}}