:root{--bg-shell: #f1f5f9;--bg-surface: #ffffff;--bg-canvas: #fcfdff;--bg-subtle: #f8fafc;--bg-hover: #f1f5f9;--border-light: #e2e8f0;--border-strong: #cbd5e1;--text-primary: #0f172a;--text-secondary: #334155;--text-muted: #64748b;--accent-blue: #2563eb;--accent-blue-soft: #eff6ff;--accent-emerald: #059669;--accent-emerald-soft: #ecfdf5;--accent-amber: #d97706;--accent-amber-soft: #fffbeb;--accent-gold: #b45309;--radius-sm: 6px;--radius-md: 10px;--shadow-sm: 0 1px 2px rgba(15, 23, 42, .04)}*,*:before,*:after{box-sizing:border-box}html,body{margin:0;padding:0;height:100%;font-family:-apple-system,BlinkMacSystemFont,Inter,Segoe UI,Roboto,PingFang SC,Hiragino Sans GB,Noto Sans CJK SC,Microsoft YaHei,Helvetica,Arial,sans-serif;color:var(--text-primary);background:var(--bg-shell);-webkit-font-smoothing:antialiased}#app{height:100vh;display:flex;flex-direction:column;overflow:hidden}.top-header{height:54px;min-height:54px;background:var(--bg-surface);border-bottom:1px solid var(--border-light);display:flex;align-items:center;justify-content:space-between;padding:0 16px;gap:12px;z-index:10}.header-left{display:flex;align-items:center;gap:12px;min-width:0}.icon-btn{display:inline-flex;align-items:center;justify-content:center;border:1px solid var(--border-light);background:var(--bg-surface);color:var(--text-secondary);border-radius:var(--radius-sm);height:32px;padding:0 10px;font-size:13px;font-weight:500;white-space:nowrap;flex-shrink:0;cursor:pointer;transition:background .14s ease,border-color .14s ease,color .14s ease}.icon-btn:hover:not(:disabled){background:var(--bg-hover);border-color:var(--border-strong);color:var(--text-primary)}.icon-btn:disabled{opacity:.42;cursor:not-allowed}.brand-group{display:inline-flex;align-items:center;gap:8px}.brand-icon{display:block;width:22px;height:22px;border-radius:5px;flex-shrink:0}.brand-title{font-size:14px;font-weight:700;letter-spacing:-.01em;color:var(--text-primary);white-space:nowrap}.header-divider{width:1px;height:20px;background:var(--border-light)}.level-breadcrumb{display:flex;align-items:center;gap:8px;min-width:0}.level-code-pill{display:inline-flex;align-items:center;padding:2px 8px;border-radius:999px;font-size:12px;font-weight:600;background:var(--accent-blue-soft);color:var(--accent-blue);border:1px solid #bfdbfe;white-space:nowrap}.level-header-title{font-size:15px;font-weight:600;color:var(--text-primary);white-space:nowrap;overflow:hidden;text-overflow:ellipsis}.header-right{display:flex;align-items:center;gap:10px;flex-shrink:0}.star-targets{display:flex;align-items:center;gap:6px}.star-target-pill{display:inline-flex;align-items:center;gap:4px;padding:3px 9px;border-radius:999px;font-size:12px;font-weight:600;background:var(--bg-subtle);color:var(--text-secondary);border:1px solid var(--border-light)}.star-target-pill.is-earned{background:var(--accent-amber-soft);color:var(--accent-gold);border-color:#fde68a}.lang-switcher{display:inline-flex;align-items:center;gap:5px;height:30px;padding:0 8px;border-radius:var(--radius-sm);border:1px solid var(--border-light);background:var(--bg-surface);color:var(--text-secondary);transition:background .14s ease,border-color .14s ease}.lang-switcher:hover{background:var(--bg-hover);border-color:var(--border-strong)}.lang-globe{font-size:13px;line-height:1;-webkit-user-select:none;user-select:none}.lang-select{border:none;background:transparent;color:var(--text-primary);font-family:inherit;font-size:12.5px;font-weight:600;padding:2px 2px 2px 0;cursor:pointer;outline:none}.workspace{--sidebar-width: 256px;--study-width: clamp(360px, 37.5%, 860px);flex:1;display:flex;flex-direction:row;min-height:0;min-width:0;overflow:hidden}.workspace.sidebar-collapsed:not(.has-custom-study-width){--study-width: clamp(380px, 42%, 880px)}.sidebar{width:var(--sidebar-width);flex:0 0 var(--sidebar-width);background:var(--bg-surface);display:flex;flex-direction:column;min-height:0;min-width:0;overflow:hidden}.workspace.sidebar-collapsed .sidebar{width:0!important;flex:0 0 0px!important}.workspace.sidebar-collapsed #resizer-sidebar{display:none}.sidebar-search-box{padding:10px 12px;border-bottom:1px solid var(--border-light)}.sidebar-search-input{width:100%;padding:6px 10px;font-size:12.5px;border:1px solid var(--border-light);border-radius:var(--radius-sm);background:var(--bg-subtle);color:var(--text-primary);outline:none}.sidebar-search-input:focus{border-color:var(--accent-blue);background:var(--bg-surface)}.sidebar-scroll{flex:1;overflow-y:auto;padding:8px}.chapter-group{margin-bottom:6px}.chapter-header-btn{width:100%;display:flex;align-items:center;justify-content:space-between;padding:7px 9px;border:none;background:transparent;border-radius:var(--radius-sm);cursor:pointer;color:var(--text-primary);font-size:13px;font-weight:600;text-align:left}.chapter-header-btn:hover{background:var(--bg-hover)}.chapter-symbol{display:inline-flex;align-items:center;justify-content:center;width:22px;height:22px;border-radius:5px;background:var(--bg-subtle);border:1px solid var(--border-light);font-family:KaTeX_Math,Georgia,serif;font-size:13px;margin-right:7px;color:var(--text-secondary)}.chapter-count{font-size:11px;font-weight:500;color:var(--text-muted)}.chapter-levels-list{padding:3px 0 4px 10px;display:flex;flex-direction:column;gap:2px}.level-nav-item{width:100%;display:flex;align-items:center;justify-content:space-between;gap:6px;padding:6px 8px;border:1px solid transparent;background:transparent;border-radius:var(--radius-sm);font-size:12.5px;color:var(--text-secondary);cursor:pointer;text-align:left}.level-nav-item:hover:not(:disabled){background:var(--bg-hover);color:var(--text-primary)}.level-nav-item.is-active{background:var(--accent-blue-soft);border-color:#bfdbfe;color:var(--accent-blue);font-weight:600}.level-nav-item:disabled{opacity:.48;cursor:default}.level-nav-code{font-size:11px;font-weight:600;min-width:26px;color:inherit;opacity:.85}.level-nav-title{flex:1;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}.level-nav-meta{font-size:10.5px;color:var(--text-muted);white-space:nowrap}.center-stage{flex:1 1 300px;min-width:300px;display:flex;flex-direction:column;min-height:0;overflow:hidden;background:var(--bg-canvas)}.problem-banner{background:var(--bg-surface);border-bottom:1px solid var(--border-light);padding:10px 16px 0}.problem-prompt{margin:0 0 10px;font-size:13.5px;line-height:1.45;color:var(--text-secondary)}.solution-tabs-row{display:flex;align-items:center;justify-content:space-between;gap:10px;flex-wrap:wrap}.solution-tabs{display:flex;align-items:center;gap:6px}.solution-tab-btn{display:inline-flex;align-items:center;gap:7px;padding:7px 13px;border:1px solid var(--border-light);border-bottom:none;border-radius:8px 8px 0 0;background:var(--bg-subtle);color:var(--text-secondary);font-size:12.5px;font-weight:600;cursor:pointer;transition:background .14s ease,color .14s ease}.solution-tab-btn:hover{background:var(--bg-hover);color:var(--text-primary)}.solution-tab-btn.is-active{background:var(--bg-canvas);color:var(--accent-blue);border-color:var(--border-strong);box-shadow:0 1px 0 var(--bg-canvas);position:relative;top:1px}.tab-star-badge{display:inline-flex;align-items:center;padding:1px 6px;border-radius:999px;font-size:11px;font-weight:700;background:#fef3c7;color:#92400e}.tab-cost-meta{font-size:11.5px;font-weight:500;color:var(--text-muted)}.canvas-wrapper{position:relative;flex:1;min-height:0;overflow:hidden;background:radial-gradient(circle at 50% 50%,#fff,#f8fafc)}.geometry-svg{display:block;width:100%;height:100%;cursor:grab;-webkit-user-select:none;user-select:none;touch-action:none}.geometry-svg.is-panning{cursor:grabbing}.svg-locus-active{animation:locusFadeIn .22s ease-out}@keyframes locusFadeIn{0%{opacity:.25}to{opacity:1}}.svg-point-label{font-family:KaTeX_Math,"Cambria Math",Times New Roman,Georgia,serif;font-style:italic;font-size:17px;fill:#0f172a;paint-order:stroke;stroke:#fcfdff;stroke-width:4.5px;stroke-linejoin:round;transition:fill .12s ease}.svg-point-label.is-constructed{fill:#1e3a8a}.svg-point-label.is-highlighted{fill:#b45309;font-weight:700}.svg-point-label.is-ghost{opacity:.75;fill:#b45309}.svg-math-sub{font-style:normal;font-family:KaTeX_Main,Georgia,serif}.svg-locus-label{font-family:KaTeX_Math,Times New Roman,Georgia,serif;font-style:italic;font-size:14px;fill:#475569;paint-order:stroke;stroke:#fcfdff;stroke-width:4px;stroke-linejoin:round}.svg-locus-label.is-highlighted{fill:#b45309;font-weight:700}.canvas-Overlay-top{position:absolute;top:10px;right:12px;display:flex;align-items:center;gap:6px;flex-wrap:wrap;justify-content:flex-end;pointer-events:none}.canvas-toolbar-card{pointer-events:auto;display:flex;align-items:center;gap:8px;padding:5px 10px;background:#ffffffeb;-webkit-backdrop-filter:blur(6px);backdrop-filter:blur(6px);border:1px solid var(--border-light);border-radius:var(--radius-sm);box-shadow:var(--shadow-sm);font-size:12px;color:var(--text-secondary)}.toolbar-check{display:inline-flex;align-items:center;gap:4px;cursor:pointer;-webkit-user-select:none;user-select:none;white-space:nowrap}.toolbar-check input{margin:0;accent-color:var(--accent-blue)}.mini-zoom-btn{border:1px solid var(--border-light);background:var(--bg-surface);color:var(--text-secondary);border-radius:4px;padding:2px 7px;font-size:12px;font-weight:600;cursor:pointer}.mini-zoom-btn:hover{background:var(--bg-hover);color:var(--text-primary)}.canvas-legend{position:absolute;bottom:10px;left:12px;display:flex;align-items:center;gap:12px;padding:4px 10px;background:#ffffffe0;border:1px solid var(--border-light);border-radius:999px;font-size:11px;color:var(--text-muted);pointer-events:none}.legend-item{display:inline-flex;align-items:center;gap:5px}.legend-swatch{width:12px;height:2.5px;border-radius:2px}.playback-bar{background:var(--bg-surface);border-top:1px solid var(--border-light);padding:10px 16px 12px;display:flex;flex-direction:column;gap:8px}.playback-controls-row{display:flex;align-items:center;flex-wrap:wrap;gap:6px}.play-primary-btn{background:var(--accent-blue);border-color:var(--accent-blue);color:#fff;min-width:76px}.play-primary-btn:hover:not(:disabled){background:#1d4ed8;border-color:#1d4ed8;color:#fff}.step-slider{flex:1 1 80px;min-width:80px;accent-color:var(--accent-blue);cursor:pointer;margin:0 4px}.step-counter-badge{font-size:12.5px;font-weight:600;color:var(--text-secondary);white-space:nowrap;flex-shrink:0;min-width:74px;text-align:right;font-variant-numeric:tabular-nums}.playback-status-row{display:flex;align-items:center;justify-content:space-between;gap:12px;font-size:12.5px}.active-step-caption{color:var(--text-secondary);overflow:hidden;text-overflow:ellipsis;white-space:nowrap}.cost-counter-group{display:flex;align-items:center;gap:8px;flex-shrink:0;font-variant-numeric:tabular-nums}.cost-pill{padding:2px 8px;border-radius:var(--radius-sm);background:var(--bg-subtle);border:1px solid var(--border-light);font-size:12px;font-weight:600;color:var(--text-secondary)}.goal-complete-pill{padding:2px 9px;border-radius:999px;background:var(--accent-emerald-soft);border:1px solid #a7f3d0;color:var(--accent-emerald);font-size:11.5px;font-weight:700}.study-column{--steps-split-ratio: .46;width:var(--study-width);flex:0 0 var(--study-width);min-width:280px;display:flex;flex-direction:column;min-height:0;background:var(--bg-surface)}.study-mode-bar{height:40px;min-height:40px;padding:0 14px;border-bottom:1px solid var(--border-light);display:flex;align-items:center;justify-content:space-between;background:var(--bg-subtle)}.study-mode-label{font-size:11.5px;font-weight:700;text-transform:uppercase;letter-spacing:.04em;color:var(--text-muted)}.view-mode-pills{display:flex;gap:4px}.mode-pill-btn{border:1px solid transparent;background:transparent;color:var(--text-muted);font-size:11.5px;font-weight:600;padding:3px 8px;border-radius:5px;cursor:pointer}.mode-pill-btn.is-active{background:var(--bg-surface);color:var(--text-primary);border-color:var(--border-light);box-shadow:var(--shadow-sm)}.steps-pane{flex:0 0 calc((100% - 45px) * var(--steps-split-ratio, .46));min-height:110px;max-height:calc(100% - 155px);display:flex;flex-direction:column;overflow:hidden}.study-column.mode-steps .steps-pane{flex:1 1 auto;max-height:none}.study-column.mode-proof .steps-pane,.study-column.mode-steps .proof-pane,.study-column.mode-steps #resizer-study-split,.study-column.mode-proof #resizer-study-split{display:none}.pane-subheader{padding:8px 14px;font-size:12px;font-weight:700;color:var(--text-secondary);background:var(--bg-surface);border-bottom:1px solid var(--border-light);display:flex;align-items:center;justify-content:space-between}.steps-list{flex:1;overflow-y:auto;padding:6px 8px;display:flex;flex-direction:column;gap:3px}.step-row{display:flex;align-items:flex-start;gap:9px;padding:7px 9px;border-radius:var(--radius-sm);border:1px solid transparent;cursor:pointer;transition:background .12s ease,border-color .12s ease}.step-row:hover{background:var(--bg-subtle)}.step-row.is-active{background:var(--accent-blue-soft);border-color:#bfdbfe}.step-row.is-future{opacity:.56}.step-row.is-hovered-sym{background:var(--accent-amber-soft);border-color:#fde68a;opacity:1}.step-num-badge{min-width:22px;height:22px;border-radius:50%;background:var(--bg-subtle);border:1px solid var(--border-light);display:inline-flex;align-items:center;justify-content:center;font-size:11px;font-weight:700;color:var(--text-secondary);margin-top:1px;flex-shrink:0}.step-row.is-active .step-num-badge{background:var(--accent-blue);border-color:var(--accent-blue);color:#fff}.step-body{flex:1;min-width:0}.step-expr-line{display:flex;align-items:center;justify-content:space-between;gap:6px}.step-entity-tag{font-family:ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;font-size:11px;color:var(--text-muted)}.step-item-expr{font-size:13px;font-weight:600;color:var(--text-primary)}.step-cost-tag{font-size:10.5px;font-weight:600;padding:1px 6px;border-radius:4px;background:var(--bg-subtle);border:1px solid var(--border-light);color:var(--text-muted);white-space:nowrap}.step-cost-tag.has-cost{color:var(--accent-blue);background:#eff6ff;border-color:#dbeafe}.step-rationale{margin-top:2px;font-size:12px;line-height:1.4;color:var(--text-muted)}.step-macro-note{margin-top:4px;font-size:11px;color:#475569;background:#f8fafc;border-left:2px solid #94a3b8;padding:3px 7px}.proof-pane{flex:1 1 110px;min-height:110px;display:flex;flex-direction:column;overflow:hidden}.proof-scroll{flex:1;overflow-y:auto;padding:14px 16px 22px;font-size:13.5px;line-height:1.68;color:var(--text-secondary)}.proof-block{margin-bottom:14px}.proof-block-label{font-size:11px;font-weight:700;text-transform:uppercase;letter-spacing:.05em;color:var(--text-muted);margin-bottom:4px}.proof-idea-callout{background:#f8fafc;border:1px solid var(--border-light);border-left:3px solid var(--accent-blue);border-radius:var(--radius-sm);padding:9px 12px;font-size:13px;color:var(--text-secondary)}.proof-single-para{margin:0}.proof-steps-ol{margin:2px 0 0;padding-left:20px;display:flex;flex-direction:column;gap:8px}.proof-steps-ol li{padding-left:3px}.proof-qed{text-align:right;font-size:13px;color:var(--text-muted);margin-top:6px}.proof-variant-note{margin-top:12px;padding:8px 11px;background:var(--accent-emerald-soft);border:1px solid #a7f3d0;border-radius:var(--radius-sm);font-size:12.5px;color:#065f46}.sym-chip{display:inline-block;padding:0 6px;margin:0 1px;border-radius:5px;border:1px solid #cbd5e1;background:#f8fafc;color:#0f172a;font-size:13px;line-height:1.4;vertical-align:baseline;cursor:pointer;transition:background .12s ease,border-color .12s ease,color .12s ease}.sym-chip-inner sub,.step-item-expr sub{font-size:.74em;line-height:0;vertical-align:-.22em}.inline-code{font-family:ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;font-size:.9em;background:#f1f5f9;border:1px solid #e2e8f0;padding:1px 5px;border-radius:4px}.sym-chip:hover,.sym-chip.is-highlighted{background:#fef3c7;border-color:#f59e0b;color:#92400e}.math-var{font-family:KaTeX_Math,"Cambria Math",Times New Roman,Georgia,serif;font-style:italic;font-weight:500}.math-fn{font-family:ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;font-size:12px;font-style:normal;color:#334155}.math-prime{font-style:normal}.pane-resizer{position:relative;z-index:6;background:var(--bg-surface);display:flex;align-items:center;justify-content:center;touch-action:none;-webkit-user-select:none;user-select:none;outline:none}.pane-resizer-col{flex:0 0 5px;width:5px;cursor:col-resize}.pane-resizer-col:before{content:"";position:absolute;top:0;bottom:0;left:2px;width:1px;background:var(--border-light);transition:background .14s ease,width .14s ease,left .14s ease,box-shadow .14s ease}#resizer-sidebar:after{content:"";position:absolute;top:0;bottom:0;left:0;right:-4px}#resizer-study:after{content:"";position:absolute;top:0;bottom:0;left:-4px;right:-4px}.pane-resizer-row{flex:0 0 5px;height:5px;cursor:row-resize}.pane-resizer-row:before{content:"";position:absolute;left:0;right:0;top:2px;height:1px;background:var(--border-light);transition:background .14s ease,height .14s ease,top .14s ease,box-shadow .14s ease}#resizer-study-split:after{content:"";position:absolute;left:0;right:0;top:-3px;bottom:-3px}.pane-resizer-grip{position:relative;z-index:1;border-radius:999px;background:var(--border-strong);opacity:.65;pointer-events:none;transition:background .14s ease,opacity .14s ease,transform .14s ease}.pane-resizer-col .pane-resizer-grip{width:3px;height:28px}.pane-resizer-row .pane-resizer-grip{width:28px;height:3px}.pane-resizer-col:hover:before,.pane-resizer-col:focus-visible:before,.pane-resizer-col.is-dragging:before{left:1px;width:3px;background:var(--accent-blue);box-shadow:0 0 0 2px #2563eb24}.pane-resizer-row:hover:before,.pane-resizer-row:focus-visible:before,.pane-resizer-row.is-dragging:before{top:1px;height:3px;background:var(--accent-blue);box-shadow:0 0 0 2px #2563eb24}.pane-resizer-col:hover .pane-resizer-grip,.pane-resizer-col:focus-visible .pane-resizer-grip,.pane-resizer-col.is-dragging .pane-resizer-grip{background:var(--accent-blue);opacity:1;transform:scaleY(1.18)}.pane-resizer-row:hover .pane-resizer-grip,.pane-resizer-row:focus-visible .pane-resizer-grip,.pane-resizer-row.is-dragging .pane-resizer-grip{background:var(--accent-blue);opacity:1;transform:scaleX(1.18)}body.is-resizing-col,body.is-resizing-col *{cursor:col-resize!important;-webkit-user-select:none!important;user-select:none!important}body.is-resizing-row,body.is-resizing-row *{cursor:row-resize!important;-webkit-user-select:none!important;user-select:none!important}
