.sidebar{background:var(--color-surface);z-index:100;border-right:1px solid var(--color-line);flex-direction:column;width:300px;max-width:100%;height:100%;transition:width .2s;display:flex;position:fixed;left:0}.sidebar.collapsed{width:60px;min-width:60px}.sidebar-inner{opacity:1;visibility:visible;pointer-events:auto;flex:1;width:100%;height:calc(100vh - 70px);padding:24px 20px 24px 24px;transition:opacity .2s;overflow:hidden auto}.sidebar-inner.collapsed{opacity:0;visibility:hidden;pointer-events:none;width:0}.return-button{color:var(--color-ink);opacity:.8;cursor:pointer;background:0 0;border:none;align-items:center;margin-bottom:18px;padding:0;font-size:15px;font-weight:400;text-decoration:none;transition:opacity .2s;display:flex}.return-button:hover{opacity:1}.return-button-arrow{margin-right:6px;font-size:18px}.contents-heading,.section-header{color:var(--color-muted)}.contents-heading{text-transform:uppercase;letter-spacing:.08em;margin-top:0;margin-bottom:18px;font-size:13px;font-weight:500}.section-header{text-transform:uppercase;letter-spacing:.09em;margin:24px 0 10px;padding-left:4px;font-size:12px;font-weight:500}.sidebar-sections{margin-top:35px}.sidebar-section{margin-bottom:0}.section-header-link{color:var(--color-body);background:0 0;border:none;border-radius:8px;align-items:center;margin-bottom:2px;padding:12px 16px;font-size:15px;font-weight:400;line-height:1.4;text-decoration:none;transition:all .15s;display:flex}.section-header-link:hover{background-color:var(--color-surface-alt);color:var(--color-ink);text-decoration:none}.section-header-link.active{background-color:var(--color-surface-alt);color:var(--color-ink);font-weight:500}.section-header-link.locked{color:var(--color-muted);background-color:#f9fafb;cursor:not-allowed!important}.section-header-link.locked:hover{color:var(--color-muted);background-color:#f9fafb}.section-header-link.locked .completion-indicator{display:none}.clean-section-title{flex:1}.completion-indicator{color:var(--color-success);margin-left:8px;font-size:14px;font-weight:600}.section-header-link.active .completion-indicator{color:var(--color-success)}.collapse-button{cursor:pointer;z-index:1000;background-color:#0000;border:none;border-radius:4px;justify-content:center;align-items:center;width:48px;height:48px;transition:all .2s;display:flex;position:absolute;top:10px}.collapse-button i{color:var(--color-muted);font-size:22px;font-weight:400}.collapse-button:hover{background-color:var(--color-surface-alt)}.collapse-button.collapsed{left:6px;right:auto}.collapse-button.expanded{right:0}.collapse-button[data-tooltip]:before{content:attr(data-tooltip);color:#fff;white-space:nowrap;opacity:0;visibility:hidden;background-color:#000c;border-radius:4px;padding:4px 8px;font-size:12px;transition:opacity .2s,visibility .2s;position:absolute;right:calc(100% + 8px);transform:translateY(-50%)}.collapse-button.collapsed[data-tooltip]:before{left:calc(100% + 8px);right:auto}.collapse-button:hover[data-tooltip]:before{opacity:1;visibility:visible}.sidebar-list-item a{color:inherit;width:100%;text-decoration:none;display:block}.sidebar-collapsed-content{opacity:1;visibility:visible;flex-direction:column;width:100%;height:calc(100vh - 70px);padding-top:60px;display:flex}.collapsed-sections{flex-direction:column;gap:8px;padding:16px 8px;display:flex}.collapsed-section-item{cursor:pointer;background-color:#0000;border:1px solid #0000;border-radius:8px;flex-direction:column;justify-content:center;align-items:center;gap:2px;width:44px;height:44px;transition:all .2s;display:flex;position:relative}.collapsed-section-item:hover,.collapsed-section-item.active,.collapsed-section-item.completed,.collapsed-section-item.active.completed{background-color:var(--color-surface-alt);border-color:#0000001a}.section-icon{color:var(--color-muted);font-size:12px;line-height:1}.collapsed-section-item.active .section-icon{color:var(--color-primary)}.collapsed-section-item.completed .section-icon{color:var(--color-success)}.lesson-count{color:var(--color-body);text-align:center;font-size:10px;font-weight:600;line-height:1}.completed-count{color:var(--color-success)}.total-count{color:var(--color-muted)}.collapsed-section-item.active .lesson-count,.collapsed-section-item.active .completed-count{color:var(--color-primary)}.collapsed-section-item.active .total-count{color:color-mix(in srgb, var(--color-primary) 45%, white)}.completion-check{color:var(--color-success);font-size:10px;position:absolute;top:2px;right:2px}.collapsed-section-item.active .completion-check{color:var(--color-primary)}.collapsed-section-item.locked{background-color:#f9fafb;border-color:#0000000d;cursor:not-allowed!important}.collapsed-section-item.locked:hover{background-color:#f9fafb;border-color:#0000000d}.collapsed-section-item.locked .section-icon,.collapsed-section-item.locked .lesson-count,.collapsed-section-item.locked .completed-count{color:var(--color-muted)}.collapsed-section-item.locked .total-count{color:#d1d5db}
@keyframes skeleton-loading{0%{background-position:-200px 0}to{background-position:calc(200px + 100%) 0}}.skeleton{background:linear-gradient(90deg,#f0f0f0 25%,#e0e0e0 50%,#f0f0f0 75%) 0 0/200px 100%;border-radius:4px;animation:1.5s infinite skeleton-loading}.loading-exercise-container{border:1px solid var(--color-line);border-radius:var(--radius-md);background:var(--color-surface);padding:20px}.loading-exercise-header{margin-bottom:24px}.loading-exercise-title.skeleton{border-radius:6px;width:60%;height:24px;margin-bottom:12px}.loading-exercise-description.skeleton{border-radius:4px;width:100%;height:16px;margin-bottom:8px}.loading-exercise-description.skeleton.short{width:75%}.loading-exercise-editor{margin-bottom:20px}.loading-editor-tabs{gap:8px;margin-bottom:12px;display:flex}.loading-tab.skeleton{border-radius:6px;width:80px;height:32px}.loading-editor-area.skeleton{background:linear-gradient(90deg,#f8f9fa 25%,#e9ecef 50%,#f8f9fa 75%) 0 0/200px 100%;border-radius:8px;width:100%;height:200px;animation:1.5s infinite skeleton-loading}.loading-exercise-controls{justify-content:space-between;align-items:center;margin-bottom:20px;display:flex}.loading-control-group{gap:12px;display:flex}.loading-run-button.skeleton{border-radius:8px;width:100px;height:40px}.loading-hint-button.skeleton{border-radius:8px;width:120px;height:40px}.loading-reset-button.skeleton{border-radius:8px;width:80px;height:40px}.loading-exercise-output{border-top:1px solid var(--color-line);padding-top:16px}.loading-output-header.skeleton{border-radius:4px;width:150px;height:20px;margin-bottom:12px}.loading-output-content.skeleton{background:linear-gradient(90deg,#f8f9fa 25%,#e9ecef 50%,#f8f9fa 75%) 0 0/200px 100%;border-radius:6px;width:100%;height:80px;animation:1.5s infinite skeleton-loading}