:root{color-scheme:light;--ink:#20252d;--muted:#7b8491;--line:#e3e7ed;--blue:#2465ed;--surface:#fff;--page:#f4f5f7;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","PingFang SC","Microsoft YaHei",sans-serif;color:var(--ink);background:var(--page);font-synthesis:none}*{box-sizing:border-box}body{margin:0}button,select,input{font:inherit}button,a,input,select{-webkit-tap-highlight-color:transparent}button,a{touch-action:manipulation}button{cursor:pointer}a{color:inherit;text-decoration:none}button:disabled{cursor:default;opacity:.32}button:focus-visible,a:focus-visible,select:focus-visible,input:focus-visible{outline:2px solid var(--blue);outline-offset:4px}button,select{color:inherit}svg{display:block}button svg,a svg{width:18px;height:18px;fill:none;stroke:currentColor;stroke-width:1.5;stroke-linecap:round;stroke-linejoin:round;flex-shrink:0}[hidden]{display:none!important}.sr-only{position:absolute;width:1px;height:1px;overflow:hidden;clip-path:inset(50%);white-space:nowrap}.reader-header{height:76px;border-bottom:1px solid var(--line);display:flex;align-items:center;justify-content:space-between;gap:30px;padding:0 max(28px,calc((100vw - 1240px)/2));background:#f7f8fa}.reader-brand{font-family:Georgia,"Songti SC",STSong,serif;font-size:24px;font-weight:600;letter-spacing:1px;white-space:nowrap}.reader-picker{max-width:460px;min-width:100px;position:relative}.reader-picker select{appearance:none;background:transparent;border:0;width:100%;font-size:14px;padding:12px 26px 12px 12px;text-overflow:ellipsis;cursor:pointer;color:#5b6470}.reader-picker>svg{position:absolute;right:4px;top:50%;transform:translateY(-50%);width:16px;height:16px;pointer-events:none;fill:none;stroke:#7b8491;stroke-width:1.5}.header-history{display:flex;gap:9px;align-items:center;white-space:nowrap;font-size:13px;color:#687280}.reader-main{max-width:1180px;margin:26px auto 40px;padding:0 20px}.problem-paper{background:var(--surface);border:1px solid var(--line);border-radius:7px;overflow:hidden}.question-top{display:flex;justify-content:space-between;align-items:baseline;gap:22px;margin:27px 32px 12px}h1{font-family:Georgia,"Songti SC",STSong,serif;font-weight:600;font-size:23px;line-height:1.5;margin:0;letter-spacing:.1px}.quiet{padding:8px 0;background:none;border:0;color:#7b8491;font-size:12px;display:inline-flex;gap:7px;align-items:center;white-space:nowrap}.quiet:hover{color:var(--blue)}.quiet svg{width:15px;height:15px}.question-body{margin:0 32px;font-family:Georgia,"Songti SC",STSong,serif;font-size:15px;line-height:1.95;overflow-wrap:anywhere}.question-body p{margin:0 0 9px;white-space:pre-line}.question-body .question-note{font-family:-apple-system,BlinkMacSystemFont,"PingFang SC",sans-serif;font-size:12px;color:var(--muted);line-height:1.8}.question-expand{margin:0 22px 0 auto;display:none}.motion-top{display:flex;align-items:center;justify-content:space-between;gap:20px;margin:17px 32px 0;padding-top:16px;border-top:1px solid #f0f1f4;font-size:12px;color:#87909c}.motion-canvas{padding:0 24px;min-width:0}#problem-scene{display:block;width:100%;height:clamp(310px,43vh,490px);background:white}.motion-events{display:flex;gap:0;overflow-x:auto;overscroll-behavior-inline:contain;margin:0 30px;scrollbar-width:thin;border-top:1px solid #eff1f4}.motion-events button{flex:1;min-width:max-content;display:flex;align-items:center;justify-content:center;gap:9px;border:0;border-bottom:2px solid transparent;background:none;min-height:61px;padding:13px 18px 15px;color:#8a919d;font-size:12px;white-space:nowrap}.motion-events button .event-number{font-size:10px;min-width:23px;height:23px;border:1px solid #e0e4eb;display:inline-flex;align-items:center;justify-content:center;border-radius:50%;font-variant-numeric:tabular-nums}.motion-events button[aria-current=true]{border-bottom-color:var(--blue);color:var(--blue)}.motion-events button[aria-current=true] .event-number{border-color:var(--blue);background:var(--blue);color:white}.motion-events button:hover{color:var(--blue)}.motion-readout{padding:17px 32px 22px;font-size:12px;line-height:1.8;color:#77808c;font-variant-numeric:tabular-nums;border-top:1px solid #eff1f4}.playback{margin-top:18px;padding:20px 25px 13px;border:1px solid var(--line);border-radius:7px;background:#fff}.playback-main{display:flex;align-items:center;gap:23px}.play-button{width:49px;height:49px;flex-shrink:0;display:grid;place-items:center;background:var(--blue);border:0;border-radius:50%;color:#fff;transition:background .15s}.play-button:hover{background:#1452db}.play-button svg{width:21px;height:21px;stroke:none;fill:currentColor}.seek-group{flex:1;min-width:0}.time-labels{display:flex;justify-content:space-between;gap:20px;color:#9099a7;font-size:11px;font-variant-numeric:tabular-nums;margin-bottom:6px}.time-labels output{color:#435772}#reader-slider{--progress:0%;appearance:none;-webkit-appearance:none;display:block;width:100%;height:24px;margin:0;cursor:pointer;background:transparent}#reader-slider::-webkit-slider-runnable-track{height:3px;border-radius:4px;background:linear-gradient(to right,var(--blue) var(--progress),#dce2ea var(--progress))}#reader-slider::-webkit-slider-thumb{appearance:none;-webkit-appearance:none;width:12px;height:12px;border-radius:50%;background:var(--blue);border:2px solid #fff;box-shadow:0 0 0 1px #b7cdfb;margin-top:-4.5px}#reader-slider::-moz-range-track{height:3px;background:#dce2ea}#reader-slider::-moz-range-progress{height:3px;background:var(--blue)}#reader-slider::-moz-range-thumb{border:2px solid #fff;width:9px;height:9px;border-radius:50%;background:var(--blue)}.speed-picker select{padding:9px 4px 9px 7px;border:1px solid var(--line);border-radius:4px;background:white;font-size:12px;color:#6f7b8d;min-height:38px}.playback-secondary{display:flex;justify-content:space-between;gap:14px;align-items:center;margin-top:8px;padding-left:72px}.step-button{display:flex;align-items:center;gap:7px;background:none;border:0;padding:8px 0;font-size:11px;color:#788598;min-height:34px}.step-button:hover{color:var(--blue)}.step-button svg{width:14px;height:14px}.event-sides{display:flex;background:#f7f8fa;border:1px solid #edf0f5;border-radius:4px;padding:2px}.event-sides button{font-size:10px;padding:5px 10px;border:0;background:none;color:#8c95a1;border-radius:3px}.event-sides button[aria-pressed=true]{background:white;color:#41608d;box-shadow:0 1px 3px #18283b12}.reader-message{font-size:14px;color:var(--muted);line-height:1.9;margin:30px 32px 40px}.reader-recovery{display:flex;gap:24px;margin:0 32px 32px}dialog{border:1px solid var(--line);border-radius:10px;box-shadow:0 20px 100px #172b4526;color:var(--ink);padding:25px;max-width:calc(100% - 32px);max-height:calc(100dvh - 40px);overflow:auto}dialog::backdrop{background:#19283955;backdrop-filter:blur(2px)}.display-dialog{width:380px}.original-dialog{width:760px}.dialog-heading{display:flex;align-items:center;justify-content:space-between;gap:20px;margin-bottom:18px}.dialog-heading h2{font-size:17px;font-weight:500;margin:0}.icon-button{display:grid;place-items:center;background:none;border:0;color:#7b8491;width:35px;height:35px}.icon-button:hover{background:#f3f5f9;border-radius:4px}.display-toggles{display:grid;gap:15px}.display-toggles label{display:flex;align-items:center;justify-content:space-between;color:#4c5c70;font-size:13px}.display-toggles input{accent-color:var(--blue);width:16px;height:16px;margin:0}.original-dialog img{display:block;max-width:100%;height:auto;margin:auto}.display-dialog .vector-controls select{max-width:190px}.display-dialog .vector-controls{font-size:12px}.display-dialog .vector-controls>label{min-height:30px}
@media(min-width:1400px){.reader-main{margin-top:30px}.question-top{margin-top:30px}#problem-scene{height:390px}}@media(max-width:700px){.reader-header{height:64px;padding:0 20px;gap:16px}.reader-brand{font-size:20px}.reader-picker{max-width:200px}.reader-picker select{font-size:12px;padding-left:0}.header-history{font-size:0;gap:0}.header-history svg{width:20px;height:20px}.reader-main{margin:16px auto 28px;padding:0 13px}.question-top{margin:20px 19px 11px;gap:13px;align-items:flex-start}h1{font-size:19px;line-height:1.6}.question-top .quiet{font-size:11px;padding-top:5px}.question-top .quiet svg{display:none}.question-body{margin:0 19px;font-size:14px;line-height:1.9}.question-body.is-collapsible:not(.expanded){max-height:106px;overflow:hidden;mask-image:linear-gradient(#000 0%,#000 72%,transparent 100%)}.question-expand:not([hidden]){display:flex;min-height:34px;font-size:11px}.motion-top{margin:10px 19px 0;padding-top:11px;font-size:11px}.motion-canvas{padding:0 8px}#problem-scene{height:clamp(255px,35vh,355px)}.motion-events{margin:0 14px}.motion-events button{font-size:11px;padding:11px 12px;min-height:54px;gap:6px}.motion-events button .event-number{height:20px;min-width:20px;font-size:9px}.playback{padding:15px 14px 8px;margin-top:12px}.playback-main{gap:13px}.play-button{width:43px;height:43px}.playback-secondary{padding-left:0;gap:10px;margin-top:6px}.step-button{min-height:40px;font-size:11px}.time-labels{font-size:10px}.speed-picker select{font-size:11px;min-height:34px}.event-sides button{padding:7px 8px}.motion-readout{font-size:11px;padding:14px 19px}.reader-message{margin:20px 19px 30px;font-size:13px}.reader-recovery{margin:0 19px 24px}dialog{padding:20px}.question-note{font-size:11px}.reader-header a{min-height:44px;display:flex;align-items:center}.reader-picker select{min-height:44px}}@media(prefers-reduced-motion:reduce){*{scroll-behavior:auto!important;transition:none!important}}
@media(min-width:701px) and (max-height:800px){.reader-header{height:64px}.reader-main{margin-top:16px;margin-bottom:18px}.question-top{margin:18px 30px 9px}h1{font-size:22px}.question-body{font-size:14px;line-height:1.85}.question-body.is-collapsible:not(.expanded){max-height:78px;overflow:hidden;mask-image:linear-gradient(#000 0%,#000 74%,transparent 100%)}.question-expand:not([hidden]){display:flex;margin-right:30px;padding:4px 0;min-height:27px}.motion-top{margin-top:8px;padding-top:8px}.motion-canvas #problem-scene{height:220px}.motion-events button{min-height:50px;padding-top:10px;padding-bottom:12px}.playback{margin-top:12px;padding-top:13px;padding-bottom:7px}.playback-secondary{margin-top:3px}.playback-main .play-button{width:44px;height:44px}}
.reader-main{max-width:1300px;display:grid;grid-template-columns:minmax(0,1fr) 268px;grid-template-areas:"paper settings" "playback playback";gap:18px;align-items:start}.problem-paper{grid-area:paper;min-width:0}.reader-settings{grid-area:settings;padding:25px 20px;background:white;border:1px solid var(--line);border-radius:7px}.reader-settings h2{font-size:16px;font-weight:500;margin:0 0 23px}.reader-settings .vector-controls{margin-top:0;padding-top:0;border-top:0;gap:18px}.reader-settings .vector-controls>label{align-items:flex-start;flex-direction:column;gap:9px}.reader-settings .vector-controls select{max-width:none;width:100%;min-height:35px}.reader-settings .vector-controls>label:has(input[type=checkbox]){flex-direction:row;align-items:center}.reader-settings .vector-controls input[type=range]{width:100%}.reader-settings .vector-scale-note{font-size:10px}.reader-settings .vector-scale-legend{gap:12px}.reader-settings .show-values{border-top:1px solid var(--line);margin-top:19px;padding-top:18px;display:flex;justify-content:space-between;align-items:center;font-size:12px;color:#68778b}.reader-settings input[type=checkbox],.quick-displays input{accent-color:var(--blue);width:14px;height:14px;flex-shrink:0;margin:0}.quick-displays{display:flex;align-items:center;gap:17px}.quick-displays label{display:flex;align-items:center;gap:7px;font-size:11px;color:#7b8491;cursor:pointer;min-height:35px}.stage-formulas{margin:0 30px;padding:17px 0 14px;border-top:1px solid #f0f2f5}.formula-line{display:flex;gap:17px 28px;flex-wrap:wrap;align-items:center}.stage-math{font-family:Georgia,"Songti SC",serif;font-size:17px;line-height:1.8;letter-spacing:.1px;color:#455a77;white-space:nowrap}.stage-math sub,.stage-math sup{font-size:.64em}.formula-note{font-size:10px;color:#969eaa;line-height:1.8;margin:7px 0 0}.playback{grid-area:playback;margin-top:0}.motion-top{margin-bottom:0}#problem-scene{height:330px}@media(min-width:1400px){#problem-scene{height:330px}}@media(min-width:701px) and (max-height:800px){.reader-main{gap:12px;grid-template-columns:minmax(0,1fr) 240px}.reader-settings{padding:20px 18px}.reader-settings .vector-controls{gap:12px}.reader-settings h2{margin-bottom:18px}.motion-canvas #problem-scene{height:195px}.stage-formulas{padding:10px 0 9px}.stage-math{font-size:15px}.formula-note{font-size:9px;margin-top:2px}.playback{margin-top:0}}@media(max-width:950px){.reader-main{display:flex;flex-direction:column;gap:13px}.problem-paper,.playback,.reader-settings{width:100%}.playback{order:2}.reader-settings{order:3;display:block}.reader-settings .vector-controls{display:grid;grid-template-columns:1fr 1fr;gap:18px 24px}.reader-settings h2{margin-bottom:20px}.reader-settings .vector-scale-note,.reader-settings .vector-scale-legend,.reader-settings .vector-values{grid-column:1/-1}.reader-settings .vector-controls>label:has(input[type=checkbox]){align-items:flex-start}.reader-settings .vector-controls select{min-width:0;max-width:100%}}@media(max-width:700px){.motion-canvas #problem-scene{height:clamp(235px,31vh,300px)}.quick-displays{gap:12px}.quick-displays label{gap:5px;font-size:10px}.stage-formulas{margin:0 19px;padding:12px 0}.formula-line{gap:6px 19px}.stage-math{font-size:15px;white-space:normal}.formula-note{font-size:10px;line-height:1.7}.reader-settings{padding:20px 18px}.reader-settings .vector-controls{gap:15px 19px}.reader-settings .vector-controls>label{font-size:11px}.playback{margin-top:0}.reader-settings h2{font-size:15px}.motion-events button{min-height:49px;padding-top:9px;padding-bottom:10px}}

.reader-vector-size{margin:0 32px 2px}.reader-vector-size .vector-gains{display:flex;gap:28px;max-width:470px;padding:3px 0 0}.reader-vector-size .vector-gains label{flex:1;min-width:0;gap:2px;font-size:11px}.reader-vector-size .vector-gains output{font-size:10px}@media(max-width:700px){.reader-vector-size{margin:0 19px}.reader-vector-size .vector-gains{gap:22px}.reader-vector-size .vector-gains label{font-size:10px}}

.symbolic-panel{margin:18px 32px 12px;border-top:1px solid #edf0f4;padding-top:16px;font-size:12px;line-height:1.9;color:#66788c}.symbolic-ratio{font-size:17px;color:#455a77;margin:0 0 14px}.symbolic-choices{display:flex;gap:10px;flex-wrap:wrap}.symbolic-choices button{display:grid;gap:6px;flex:1;min-width:130px;text-align:left;border:1px solid #e0e6ef;border-radius:5px;padding:11px 13px;background:white;color:#6e7b8e;font-size:12px}.symbolic-choices button[aria-pressed=true]{border-color:#2465ed;background:#f3f7ff;color:#2465ed}.symbolic-claims{display:flex;gap:12px 28px;flex-wrap:wrap;font-size:16px;color:#455a77;margin-top:18px}.symbolic-panel details{padding:2px 0}.symbolic-panel summary{cursor:pointer;color:#6e7b8e}.symbolic-panel details>div{margin:12px 0;overflow-x:auto}.symbolic-panel details>div p{font-size:11px;margin:8px 0}.symbolic-preview-note{color:#98a2ae;font-size:11px}.symbolic-mode .vector-scale-legend,.symbolic-mode .vector-values,.symbolic-mode .show-values{display:none}.symbolic-mode .vector-scale-note{font-size:0}.symbolic-mode .vector-scale-note:after{content:'箭头按本分支代表性比例示意；分量仍沿物理坐标轴。';font-size:11px}@media(max-width:700px){.symbolic-panel{margin:14px 19px 10px}.symbolic-choices{gap:7px}.symbolic-choices button{min-width:90px;padding:10px 6px;font-size:10px}.symbolic-claims{font-size:14px;gap:12px}.symbolic-preview-note{font-size:10px}}