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p{margin:0;color:#cbd5e1;font-size:.9rem}.navigation-section{display:flex;justify-content:space-between;gap:1rem;margin-top:2rem;padding-top:2rem;border-top:1px solid rgba(34,197,94,.2)}.nav-btn{padding:.75rem 1.5rem;border-radius:8px;font-weight:600;text-decoration:none;transition:all .2s}.nav-btn.prev{background:#22c55e1a;border:1px solid rgba(34,197,94,.3);color:#86efac}.nav-btn.next{background:linear-gradient(135deg,#22c55e4d,#16a34a4d);border:1px solid rgba(34,197,94,.5);color:#86efac}.nav-btn:hover{transform:translateY(-2px);box-shadow:0 4px 12px #22c55e33}@media(max-width:768px){.problem-title-row h1{font-size:1.5rem}.navigation-section{flex-direction:column}.nav-btn{text-align:center}}.sidebar{width:280px;height:calc(100vh - 70px);background:var(--bg-card);border-right:1px solid var(--border);position:sticky;top:70px;overflow-y:auto;transition:width var(--transition-normal);display:flex;flex-direction:column;-webkit-backdrop-filter:blur(12px);backdrop-filter:blur(12px);z-index:10}.sidebar.collapsed{width:60px}.sidebar-header{padding:var(--spacing-md);display:flex;align-items:center;justify-content:space-between;border-bottom:1px solid var(--border)}.sidebar-title{font-weight:700;font-size:1.1rem;color:var(--text-primary);white-space:nowrap;overflow:hidden;opacity:1;transition:opacity var(--transition-fast)}.sidebar.collapsed .sidebar-title{opacity:0;width:0}.toggle-btn{padding:var(--spacing-xs);border-radius:var(--radius-md);color:var(--text-secondary);background:transparent;display:flex;align-items:center;justify-content:center}.toggle-btn:hover{background:var(--bg-tertiary);color:var(--primary)}.sidebar-content{padding:var(--spacing-md);flex:1;overflow-x:hidden}.topic-group{margin-bottom:var(--spacing-sm)}.topic-header{width:100%;display:flex;align-items:center;justify-content:space-between;padding:var(--spacing-sm);border-radius:var(--radius-md);color:var(--text-secondary);font-weight:500;cursor:pointer;transition:all var(--transition-fast);background:transparent;text-align:left}.topic-header:hover{background:var(--bg-tertiary);color:var(--text-primary)}.topic-header.active{color:var(--primary);background:var(--primary-light)}.topic-icon{display:flex}.topic-label{flex:1;margin-left:var(--spacing-sm);white-space:nowrap}.sidebar.collapsed .topic-label,.sidebar.collapsed .chevron{display:none}.sidebar.collapsed .topic-header{justify-content:center;padding:var(--spacing-sm) 0}.sidebar.collapsed .topic-icon{margin:0}.topic-list{margin-left:var(--spacing-lg);margin-top:var(--spacing-xs);display:flex;flex-direction:column;gap:var(--spacing-xs);border-left:2px solid var(--border);padding-left:var(--spacing-sm)}.sidebar.collapsed .topic-list{display:none}.topic-link{padding:var(--spacing-xs) var(--spacing-sm);color:var(--text-secondary);font-size:.9rem;border-radius:var(--radius-md);transition:all var(--transition-fast);white-space:nowrap;overflow:hidden;text-overflow:ellipsis;display:block}.topic-link:hover{color:var(--text-primary);background:var(--bg-tertiary);transform:translate(4px)}.topic-link.active{color:var(--primary);background:var(--bg-tertiary);font-weight:500;border-right:3px solid var(--primary)}.chevron{transition:transform var(--transition-normal)}.chevron.expanded{transform:rotate(180deg)}.sidebar::-webkit-scrollbar{width:4px}.sidebar::-webkit-scrollbar-thumb{background:var(--border)}.app-container{display:flex;min-height:calc(100vh - 70px)}.main-content{flex:1;padding:0;width:100%;display:flex;flex-direction:column}.main-content>*:first-child{flex:1}@media(max-width:768px){.app-container{flex-direction:column}}