:root{color-scheme:light;--bg:#f4f7fb;--surface:#fff;--text:#172033;--muted:#667085;--border:#d8e1ee;--primary:#155eef;--soft:#eaf2ff;--one:#1565d8;--two:#9a6700;--good:#16794b;--warn:#a65f00;--rail:180px;font-family:"Microsoft YaHei UI","Microsoft YaHei",sans-serif;color:var(--text);background:var(--bg)}
*{box-sizing:border-box}body{margin:0;height:100vh;min-width:320px;overflow:hidden}button,input,select{font:inherit;color:inherit}button{cursor:pointer;min-height:38px;border:1px solid var(--border);border-radius:8px;background:var(--surface);font-weight:700}button:hover:not(:disabled){background:var(--soft);border-color:#b9d1ff}button:disabled{opacity:.48;cursor:default}button:focus-visible,input:focus-visible,select:focus-visible,[tabindex]:focus-visible{outline:3px solid rgba(124,58,237,.55);outline-offset:-3px}input{accent-color:var(--primary)}
#app{height:100vh;padding:16px}.app-shell{height:100%;display:grid;grid-template-columns:minmax(0,1fr) var(--rail);grid-template-rows:78px minmax(0,1fr);gap:12px}.equation-bar,.canvas-panel,.control-panel{min-width:0;background:var(--surface);border:1px solid var(--border);border-radius:12px;box-shadow:0 6px 18px #1e40af14}
.equation-bar{display:flex;align-items:center;gap:12px;padding:8px 12px;overflow:hidden}.balance-state{display:flex;align-items:center;justify-content:center;gap:7px;white-space:nowrap;color:var(--good);background:#eaf8f1;border-radius:24px;min-width:80px;padding:10px;font-size:14px}.balance-state.is-unbalanced{color:var(--warn);background:#fff4e5}.state-dot{height:8px;width:8px;border-radius:50%;background:currentColor}.equation-content{min-width:0;flex:1;border-left:1px solid var(--border);padding-left:12px;font-weight:700}.quantity-values{display:flex;justify-content:center;gap:18px;font-size:13px;white-space:nowrap}.term-one{color:var(--one)}.term-two{color:var(--two)}.equation-expressions{display:flex;align-items:center;justify-content:center;gap:20px;font-size:11px;line-height:1.65;margin-top:4px}.caption{color:var(--muted)}.direction-note,.rounding-note{font-size:10px;color:var(--warn);margin-left:4px}.data-formula,.physical-formula{white-space:nowrap}
.canvas-panel{grid-column:1;grid-row:2;display:grid;grid-template-rows:auto minmax(0,1fr) 48px;overflow:hidden}.canvas-heading{padding:12px 18px;border-bottom:1px solid #edf1f7;display:flex;justify-content:space-between;gap:10px}.canvas-heading p{font-size:18px;font-weight:800;margin:0 0 3px}.canvas-heading small{font-size:11px;color:var(--muted)}.experiment-viewport{min-height:0;min-width:0;overflow:scroll;overscroll-behavior:contain;position:relative}.canvas-stage{position:relative;overflow:hidden}.lever-canvas{position:absolute;display:block;user-select:none;touch-action:pan-x pan-y}.zoom-bar{border-top:1px solid #edf1f7;display:flex;align-items:center;justify-content:flex-end;gap:8px;padding:4px 12px;background:var(--surface);font-size:12px}.zoom-bar label{color:var(--muted);margin-right:auto}.zoom-bar input{min-width:60px;width:120px}.zoom-bar button{min-width:36px;min-height:34px}.zoom-bar output{min-width:38px;font-variant-numeric:tabular-nums}.zoom-bar .zoom-reset{font-weight:400;font-size:11px;padding:0 8px}
.control-panel{grid-column:2;grid-row:1/-1;overflow:auto;padding:12px 10px;display:flex;flex-direction:column;gap:12px}.control-panel h2{margin:0;padding-bottom:10px;border-bottom:1px solid #edf1f7;font-size:16px}.control-group{min-width:0}.control-group h3,.slot-card h3{margin:0 0 6px;font-size:11px;color:var(--muted)}.segmented{display:grid;grid-template-columns:1fr 1fr;gap:3px;background:var(--bg);padding:2px;border:1px solid var(--border);border-radius:10px}.segmented button{border:0;background:transparent;font-size:11px;min-height:40px;font-weight:700;padding:4px}.segmented button.is-active{background:var(--primary);color:#fff}.segmented button.is-active:hover{background:var(--primary);color:#fff}.hook-source{width:100%;height:64px;background:var(--soft);color:var(--primary);border-color:#b9d1ff;cursor:grab;touch-action:none;display:flex;align-items:center;justify-content:center;gap:10px}.hook-source strong{font-size:18px}.hook-source small{font-size:11px;color:var(--muted)}.control-hint{font-size:10px;line-height:1.5;color:var(--muted);margin:5px 0 0}.slot-card{border:1px solid var(--border);border-radius:10px;padding:8px;margin-bottom:8px}.slot-card.is-selected{border-color:var(--primary);box-shadow:0 0 0 1px #b9d1ff}.slot-heading{display:flex;align-items:center;justify-content:space-between;margin-bottom:6px}.slot-heading button{border:0;padding:0;min-height:28px;background:transparent;color:var(--one);font-size:14px}.slot-card[data-slot="free-two"] .slot-heading button{color:var(--two)}.slot-heading small{font-size:9px;color:var(--muted)}.slot-card .segmented button{min-height:36px;font-size:10px}.count-control{display:grid;grid-template-columns:36px 1fr 36px;align-items:center;gap:3px;text-align:center;margin-top:8px;font-size:13px}.count-control button{min-height:36px}.position-control{display:flex;align-items:center;justify-content:space-between;font-size:10px;color:var(--muted);margin-top:8px;gap:4px}.position-control input{width:70px;min-height:30px;border:1px solid var(--border);border-radius:5px;padding:2px 3px;background:#fff;text-align:right;color:var(--text)}.gravity-options{display:flex;gap:12px;font-size:12px}.gravity-options label,.compact-toggle{display:flex;align-items:center;gap:5px;min-height:32px}.gravity-options input,.compact-toggle input{width:17px;height:17px}.compact-toggle{font-size:11px}.control-actions{margin-top:auto;border-top:1px solid #edf1f7;padding-top:12px;display:grid;gap:7px}.control-actions button{font-size:12px;min-height:42px}.control-actions .primary-button{background:var(--primary);color:#fff;border-color:var(--primary)}.control-actions .primary-button:hover{background:#174bcb}.edit-hint{margin:0;padding:7px;background:#fff4e5;border-radius:6px;font-size:10px;line-height:1.5;color:var(--warn)}
.control-panel::-webkit-scrollbar{width:6px}.experiment-viewport::-webkit-scrollbar{width:10px;height:10px}.control-panel::-webkit-scrollbar-thumb,.experiment-viewport::-webkit-scrollbar-thumb{background:#98a2b3;border:2px solid var(--bg);border-radius:8px}.control-panel::-webkit-scrollbar-track,.experiment-viewport::-webkit-scrollbar-track{background:var(--bg)}
.lever-bar{stroke:#111827;stroke-width:9;stroke-linecap:round}.slot line,.slot circle{stroke:#98a2b3;fill:#98a2b3}.pivot{fill:white;stroke:#111827;stroke-width:4}.pivot-base{stroke:#111827;stroke-width:4}.pivot-dot{fill:#111827}.pivot-label{font-size:20px;font-weight:700}.force-one{color:var(--one)}.force-two{color:var(--two)}#arrow-one{fill:var(--one)}#arrow-two{fill:var(--two)}.action-line{stroke:currentColor;stroke-width:2;stroke-dasharray:7 7;opacity:.7}.arm-halo{stroke:#fff;stroke-width:12}.arm-line{stroke:currentColor;stroke-width:3}.right-angle,.hanger{fill:none;stroke:currentColor;stroke-width:2}.force-arrow{stroke:currentColor;stroke-width:4}.force-point{fill:currentColor;stroke:white;stroke-width:2}.force-endpoint{fill:white;stroke:currentColor;stroke-width:3}.force-label,.arm-label,.count-label{fill:currentColor;font-size:16px;font-weight:700;pointer-events:none}.hook-block{stroke:currentColor;stroke-width:3;fill:white;cursor:grab;touch-action:none}.hook-force .force-point{cursor:grab;touch-action:none}.is-selected .force-point{r:8}.force-handle-zone{fill:transparent;stroke:transparent;cursor:grab;touch-action:none}.force-handle-zone:hover,.force-handle-zone:focus-visible{stroke:currentColor;stroke-width:1;stroke-opacity:.6}.force-handle-zone[data-free-part="endpoint"]{cursor:crosshair}.snap-ring{stroke:var(--good);stroke-width:3;fill:none;stroke-dasharray:4 3;pointer-events:none}.drag-ghost{position:fixed;pointer-events:none;z-index:20;background:var(--soft);color:var(--primary);border:2px solid var(--primary);border-radius:22px;padding:6px 12px;transform:translate(-50%,-50%);font-weight:700}.is-press-pending{stroke-width:5}
@media(max-width:1000px){.equation-expressions{display:block;text-align:center;font-size:10px;margin-top:2px}.quantity-values{gap:10px;font-size:11px}.equation-bar{padding:6px 9px;gap:8px}.equation-content{padding-left:8px}.balance-state{min-width:64px;font-size:11px;padding:9px}.direction-note{font-size:9px}.canvas-heading{padding:10px 12px}.zoom-bar{gap:5px;padding-inline:8px}.zoom-bar input{width:96px}.zoom-bar label{font-size:11px}}
@media(max-width:760px){:root{--rail:166px}#app{padding:10px}.app-shell{gap:8px}.control-panel{padding:10px 8px}.quantity-values{gap:6px;font-size:10px}.equation-content{padding-left:6px}.data-formula,.physical-formula{font-size:9px}.direction-note{font-size:8px}.canvas-heading p{font-size:16px}.zoom-bar label{display:none}.zoom-bar{justify-content:center}.slot-card{padding:6px}.position-control input{width:63px}}

/* Decoration must not steal touch gestures from the handles beneath it. */
.lever-bar,.guide-slots,.pivot,.pivot-base,.pivot-dot,.pivot-label,.action-line,.arm-halo,.arm-line,.right-angle,.hanger,.force-arrow{pointer-events:none}
.hook-body-zone{fill:transparent;stroke:none;cursor:grab;touch-action:none}
button,label,input{touch-action:manipulation}
@media(pointer:coarse){
  .canvas-stage{touch-action:none}
  button,.segmented button,.slot-card .segmented button,.count-control button,.zoom-bar button,.control-actions button{min-height:44px}
  .count-control{grid-template-columns:44px 1fr 44px}
  .compact-toggle,.gravity-options label{min-height:44px;display:flex;align-items:center}
  .position-control input{min-height:44px;font-size:14px}
  .slot-heading button{min-height:44px}
}
@media(pointer:coarse) and (orientation:landscape) and (max-height:540px){
  :root{--rail:184px}
  #app{padding:6px;height:100vh;height:100dvh}
  .app-shell{grid-template-rows:64px minmax(0,1fr);gap:6px}
  .equation-bar{padding:4px 8px;gap:6px;border-radius:8px}
  .balance-state{min-width:54px;padding:7px 5px;font-size:12px;gap:4px}
  .equation-content{padding-left:6px}
  .quantity-values{gap:8px;font-size:11px}
  .equation-expressions{display:flex;flex-wrap:wrap;gap:0 12px;margin-top:3px;font-size:11px;line-height:1.35}
  .data-formula,.physical-formula{font-size:11px}
  .direction-note,.rounding-note{font-size:10px}
  .canvas-panel{grid-template-rows:32px minmax(0,1fr) 48px;border-radius:8px}
  .canvas-heading{padding:5px 9px;align-items:center}
  .canvas-heading>div{display:flex;gap:10px;align-items:center;min-width:0}
  .canvas-heading p{font-size:14px;margin:0;white-space:nowrap}
  .canvas-heading small{font-size:10px;white-space:nowrap}
  .zoom-bar{justify-content:center;gap:4px;padding:2px 6px}
  .zoom-bar label{display:none}
  .zoom-bar input{width:76px;min-width:54px;height:44px}
  .zoom-bar button{min-width:44px;padding:0 4px}
  .zoom-bar .zoom-reset{font-size:11px;padding:0 6px}
  .control-panel{padding:8px;gap:10px;border-radius:8px}
  .control-panel h2{font-size:14px;padding-bottom:7px}
  .control-group h3,.slot-card h3{font-size:11px;margin-bottom:4px}
  .segmented button,.slot-card .segmented button{font-size:12px}
  .hook-source{height:52px}
  .control-hint{font-size:11px;line-height:1.5}
  .force-label,.arm-label,.count-label{font-size:var(--diagram-label-size,16px)}
  .experiment-viewport::-webkit-scrollbar{width:6px;height:6px}
}
@media(pointer:coarse) and (orientation:landscape) and (max-height:540px) and (max-width:700px){
  :root{--rail:172px}
  .quantity-values{display:grid;grid-template-columns:1fr 1fr;gap:1px 8px;text-align:center;font-size:11px}
  .equation-expressions{font-size:10px;margin-top:1px;gap:0 6px}
  .physical-formula,.data-formula{font-size:10px}
  .physical-formula .caption{display:none}
  .canvas-heading small{display:none}
}