:root{--primary: #4A90D9;--primary-dark: #357ABD;--secondary: #FF6B6B;--accent: #4ECDC4;--accent2: #45B7D1;--bg: #F7F9FC;--bg-card: #FFFFFF;--text: #2C3E50;--text-light: #7F8C8D;--border: #E1E8ED;--success: #27AE60;--warning: #F39C12;--danger: #E74C3C;--shadow: 0 2px 8px rgba(0, 0, 0, .08);--shadow-lg: 0 4px 20px rgba(0, 0, 0, .12);--radius: 12px;--radius-sm: 8px;--transition: .2s ease}*{margin:0;padding:0;box-sizing:border-box}body{font-family:Segoe UI,system-ui,-apple-system,sans-serif;background:var(--bg);color:var(--text);line-height:1.6}a{color:var(--primary);text-decoration:none}a:hover{color:var(--primary-dark)}.main-nav,.admin-nav{background:#fff;box-shadow:var(--shadow);position:sticky;top:0;z-index:100}.admin-nav{background:var(--text)}.admin-nav .logo-text,.admin-nav .nav-link{color:#fff}.nav-container{max-width:1200px;margin:0 auto;padding:0 24px;display:flex;align-items:center;justify-content:space-between;height:60px}.logo{display:flex;align-items:center;gap:8px;font-size:1.25rem;font-weight:700;color:var(--text);text-decoration:none}.logo-icon{font-size:1.5rem}.nav-links{display:flex;align-items:center;gap:8px}.nav-link{padding:8px 16px;border-radius:var(--radius-sm);color:var(--text);font-weight:500;transition:var(--transition)}.nav-link:hover{background:var(--bg);color:var(--primary)}.nav-link.router-link-exact-active{background:var(--primary);color:#fff}.admin-link{border:1px solid var(--border)}.btn-logout{padding:8px 16px;border:none;border-radius:var(--radius-sm);background:var(--danger);color:#fff;font-weight:500;cursor:pointer;transition:var(--transition)}.btn-logout:hover{opacity:.9}.main-content{min-height:calc(100vh - 120px)}.main-footer{background:#fff;border-top:1px solid var(--border);padding:20px 0;text-align:center;color:var(--text-light);font-size:.875rem}.footer-container{max-width:1200px;margin:0 auto;padding:0 24px}.container{max-width:1200px;margin:0 auto;padding:32px 24px}.card{background:var(--bg-card);border-radius:var(--radius);box-shadow:var(--shadow);padding:24px;transition:var(--transition)}.card:hover{box-shadow:var(--shadow-lg);transform:translateY(-2px)}.card-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:20px}.grade-card{cursor:pointer;border-left:4px solid var(--primary)}.grade-card .grade-icon{font-size:2.5rem;margin-bottom:12px}.grade-card h2{font-size:1.5rem;margin-bottom:8px}.grade-card p{color:var(--text-light);font-size:.9rem;margin-bottom:12px}.grade-card .topic-count{display:inline-block;padding:4px 12px;background:var(--bg);border-radius:20px;font-size:.8rem;color:var(--text-light);font-weight:500}.topic-card{cursor:pointer}.topic-card .topic-header{display:flex;align-items:center;gap:12px;margin-bottom:8px}.topic-card .topic-icon{font-size:1.5rem}.topic-card h3{font-size:1.1rem;flex:1}.topic-card p{color:var(--text-light);font-size:.85rem;margin-bottom:12px}.topic-card .activity-badge{display:inline-block;padding:4px 10px;background:var(--accent);color:#fff;border-radius:20px;font-size:.75rem;font-weight:600}.activity-card{display:flex;align-items:center;gap:16px;cursor:pointer}.activity-card .activity-type-icon{font-size:1.8rem;width:50px;height:50px;display:flex;align-items:center;justify-content:center;background:var(--bg);border-radius:var(--radius-sm);flex-shrink:0}.activity-card .activity-info{flex:1}.activity-card h4{font-size:1rem;margin-bottom:4px}.activity-card .activity-meta{display:flex;gap:12px;font-size:.8rem;color:var(--text-light)}.activity-card .difficulty{padding:2px 8px;border-radius:12px;font-size:.7rem;font-weight:600;text-transform:uppercase}.difficulty.easy{background:#d5f5e3;color:var(--success)}.difficulty.medium{background:#fdebd0;color:var(--warning)}.difficulty.hard{background:#fadbd8;color:var(--danger)}.btn{display:inline-flex;align-items:center;gap:8px;padding:10px 24px;border:none;border-radius:var(--radius-sm);font-size:.95rem;font-weight:600;cursor:pointer;transition:var(--transition)}.btn-primary{background:var(--primary);color:#fff}.btn-primary:hover{background:var(--primary-dark)}.btn-secondary{background:var(--bg);color:var(--text);border:1px solid var(--border)}.btn-secondary:hover{background:var(--border)}.btn-danger{background:var(--danger);color:#fff}.btn-danger:hover{opacity:.9}.btn-success{background:var(--success);color:#fff}.btn-sm{padding:6px 14px;font-size:.85rem}.btn-block{width:100%;justify-content:center}.form-group{margin-bottom:16px}.form-group label{display:block;margin-bottom:6px;font-weight:600;font-size:.9rem}.form-control{width:100%;padding:10px 14px;border:1px solid var(--border);border-radius:var(--radius-sm);font-size:.95rem;transition:var(--transition)}.form-control:focus{outline:none;border-color:var(--primary);box-shadow:0 0 0 3px #4a90d926}select.form-control{-webkit-appearance:none;-moz-appearance:none;appearance:none;background-image:url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 12 12'%3E%3Cpath d='M6 8L1 3h10z' fill='%237F8C8D'/%3E%3C/svg%3E");background-repeat:no-repeat;background-position:right 12px center;padding-right:36px}textarea.form-control{resize:vertical;min-height:80px}.page-header{margin-bottom:28px}.page-header h1{font-size:2rem;margin-bottom:8px}.page-header p{color:var(--text-light);font-size:1rem}.breadcrumb{display:flex;align-items:center;gap:8px;margin-bottom:12px;font-size:.9rem;color:var(--text-light)}.breadcrumb a{color:var(--primary)}.breadcrumb span{color:var(--text-light)}.stats-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(200px,1fr));gap:16px;margin-bottom:28px}.stat-card{background:var(--bg-card);border-radius:var(--radius);box-shadow:var(--shadow);padding:20px;text-align:center}.stat-card .stat-value{font-size:2.2rem;font-weight:700;color:var(--primary)}.stat-card .stat-label{font-size:.85rem;color:var(--text-light);margin-top:4px}.chart-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(400px,1fr));gap:20px;margin-bottom:28px}.chart-card{background:var(--bg-card);border-radius:var(--radius);box-shadow:var(--shadow);padding:24px}.chart-card h3{font-size:1.1rem;margin-bottom:16px}.table-container{background:var(--bg-card);border-radius:var(--radius);box-shadow:var(--shadow);overflow-x:auto}table{width:100%;border-collapse:collapse}th,td{padding:12px 16px;text-align:left;border-bottom:1px solid var(--border)}th{background:var(--bg);font-weight:600;font-size:.85rem;color:var(--text-light);text-transform:uppercase;letter-spacing:.5px}tr:hover{background:var(--bg)}tr:last-child td{border-bottom:none}.activity-content{max-width:800px;margin:0 auto}.activity-header{background:var(--bg-card);border-radius:var(--radius);box-shadow:var(--shadow);padding:32px;margin-bottom:24px;text-align:center}.activity-header .activity-icon{font-size:3rem;margin-bottom:16px}.activity-header h1{font-size:1.8rem;margin-bottom:8px}.activity-header .activity-meta-badges{display:flex;justify-content:center;gap:12px;margin-top:16px}.activity-body{background:var(--bg-card);border-radius:var(--radius);box-shadow:var(--shadow);padding:32px}.login-container{display:flex;justify-content:center;align-items:center;min-height:80vh}.login-card{background:var(--bg-card);border-radius:var(--radius);box-shadow:var(--shadow-lg);padding:40px;width:100%;max-width:420px}.login-card h1{text-align:center;margin-bottom:8px;font-size:1.5rem}.login-card .login-subtitle{text-align:center;color:var(--text-light);margin-bottom:28px}.empty-state{text-align:center;padding:60px 20px;color:var(--text-light)}.empty-state .empty-icon{font-size:3rem;margin-bottom:16px}.empty-state h3{font-size:1.2rem;margin-bottom:8px;color:var(--text)}.filter-bar{display:flex;gap:12px;margin-bottom:24px;flex-wrap:wrap;align-items:center}.filter-bar select{width:auto;min-width:180px}.alert{padding:12px 16px;border-radius:var(--radius-sm);margin-bottom:16px;font-size:.9rem}.alert-error{background:#fadbd8;color:var(--danger);border:1px solid #F1948A}.alert-success{background:#d5f5e3;color:var(--success);border:1px solid #82E0AA}.modal-overlay{position:fixed;top:0;left:0;right:0;bottom:0;background:#00000080;display:flex;justify-content:center;align-items:center;z-index:200;padding:20px}.modal{background:#fff;border-radius:var(--radius);box-shadow:var(--shadow-lg);width:100%;max-width:600px;max-height:90vh;overflow-y:auto}.modal-header{padding:20px 24px;border-bottom:1px solid var(--border);display:flex;align-items:center;justify-content:space-between}.modal-header h2{font-size:1.25rem}.modal-header .btn-close{background:none;border:none;font-size:1.5rem;cursor:pointer;color:var(--text-light)}.modal-body{padding:24px}.modal-footer{padding:16px 24px;border-top:1px solid var(--border);display:flex;justify-content:flex-end;gap:10px}@media (max-width: 768px){.nav-links{gap:4px}.nav-link{padding:6px 10px;font-size:.85rem}.card-grid{grid-template-columns:1fr}.stats-grid{grid-template-columns:repeat(2,1fr)}.chart-grid{grid-template-columns:1fr}.page-header h1{font-size:1.5rem}}