:root {
    /* Color System */
    --primary: #3b82f6;
    --primary-dark: #2563eb;
    --secondary: #8b5cf6;
    --success: #10b981;
    --danger: #ef4444;
    --warning: #f59e0b;
    --info: #06b6d4;
    
    /* Neutral Colors */
    --bg-main: #f8fafc;
    --bg-card: #ffffff;
    --bg-sidebar: #1e293b;
    --bg-header: #ffffff;
    
    /* Text Colors */
    --text-primary: #0f172a;
    --text-secondary: #64748b;
    --text-light: #94a3b8;
    --text-white: #ffffff;
    
    /* Border & Shadow */
    --border: #e2e8f0;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1);
    
    /* Spacing */
    --sidebar-width: 260px;
    --header-height: 64px;
    
    /* Typography */
    --font-base: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', sans-serif;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: var(--font-base);
    background: var(--bg-main);
    color: var(--text-primary);
    line-height: 1.6;
}

/* Layout Structure */
.app-container {
    display: flex;
    min-height: 100vh;
}

/* Sidebar Styles */
.sidebar {
    width: var(--sidebar-width);
    background: var(--bg-sidebar);
    position: fixed;
    height: 100vh;
    overflow-y: auto;
    transition: transform 0.3s ease;
    z-index: 1000;
}

.sidebar.collapsed {
    transform: translateX(-100%);
}

.sidebar-logo {
    padding: 20px;
    border-bottom: 1px solid rgba(255, 255, 255, 0.1);
}

.sidebar-logo h2 {
    color: var(--text-white);
    font-size: 20px;
    font-weight: 700;
}

.sidebar-menu {
    padding: 20px 0;
}

.menu-item {
    display: flex;
    align-items: center;
    padding: 12px 20px;
    color: var(--text-light);
    text-decoration: none;
    transition: all 0.2s;
    font-size: 15px;
}

.menu-item:hover {
    background: rgba(255, 255, 255, 0.05);
    color: var(--text-white);
}

.menu-item.active {
    background: var(--primary);
    color: var(--text-white);
    border-right: 3px solid var(--primary-dark);
}

.menu-item svg {
    width: 20px;
    height: 20px;
    margin-right: 12px;
}

/* Main Content */
.main-content {
    flex: 1;
    margin-left: var(--sidebar-width);
    transition: margin-left 0.3s ease;
}

.main-content.expanded {
    margin-left: 0;
}

/* Header */
.header {
    background: var(--bg-header);
    height: var(--header-height);
    border-bottom: 1px solid var(--border);
    display: flex;
    align-items: center;
    padding: 0 30px;
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: var(--shadow-sm);
}

.header-left {
    display: flex;
    align-items: center;
    gap: 20px;
}

.hamburger {
    display: none;
    flex-direction: column;
    gap: 4px;
    cursor: pointer;
    padding: 8px;
}

.hamburger span {
    width: 24px;
    height: 2px;
    background: var(--text-primary);
    border-radius: 2px;
    transition: 0.3s;
}

.page-title {
    font-size: 24px;
    font-weight: 700;
    color: var(--text-primary);
}

.header-right {
    margin-left: auto;
    display: flex;
    align-items: center;
    gap: 15px;
}

.user-info {
    display: flex;
    align-items: center;
    gap: 10px;
}

.user-avatar {
    width: 36px;
    height: 36px;
    border-radius: 50%;
    background: var(--primary);
    color: white;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 600;
    font-size: 14px;
}

.user-name {
    font-size: 14px;
    font-weight: 500;
    color: var(--text-primary);
}

/* Content Area */
.content {
    padding: 30px;
}

/* Cards */
.card {
    background: var(--bg-card);
    border-radius: 12px;
    box-shadow: var(--shadow);
    border: 1px solid var(--border);
    overflow: hidden;
}

.card-header {
    padding: 20px;
    border-bottom: 1px solid var(--border);
}

.card-title {
    font-size: 18px;
    font-weight: 600;
    color: var(--text-primary);
}

.card-body {
    padding: 20px;
}

/* Stats Grid */
.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
    gap: 20px;
    margin-bottom: 30px;
}

.stat-card {
    background: var(--bg-card);
    padding: 20px;
    border-radius: 12px;
    border: 1px solid var(--border);
    box-shadow: var(--shadow);
    transition: transform 0.2s, box-shadow 0.2s;
}

.stat-card:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.stat-icon {
    width: 48px;
    height: 48px;
    border-radius: 10px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 12px;
    font-size: 24px;
}

.stat-icon.blue { background: rgba(59, 130, 246, 0.1); color: var(--primary); }
.stat-icon.green { background: rgba(16, 185, 129, 0.1); color: var(--success); }
.stat-icon.purple { background: rgba(139, 92, 246, 0.1); color: var(--secondary); }
.stat-icon.red { background: rgba(239, 68, 68, 0.1); color: var(--danger); }

.stat-value {
    font-size: 32px;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 4px;
}

.stat-label {
    font-size: 14px;
    color: var(--text-secondary);
}

/* Buttons */
.btn {
    display: inline-block;
    padding: 10px 20px;
    border-radius: 8px;
    font-weight: 500;
    text-decoration: none;
    border: none;
    cursor: pointer;
    transition: all 0.2s;
    font-size: 14px;
    text-align: center;
}

.btn-primary {
    background: var(--primary);
    color: white;
}

.btn-primary:hover {
    background: var(--primary-dark);
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

.btn-success {
    background: var(--success);
    color: white;
}

.btn-success:hover {
    background: #059669;
}

.btn-danger {
    background: var(--danger);
    color: white;
}

.btn-danger:hover {
    background: #dc2626;
}

.btn-secondary {
    background: var(--text-secondary);
    color: white;
}

/* Badges */
.badge {
    display: inline-block;
    padding: 4px 12px;
    border-radius: 12px;
    font-size: 12px;
    font-weight: 600;
}

.badge-success { background: #d1fae5; color: #065f46; }
.badge-warning { background: #fef3c7; color: #92400e; }
.badge-danger { background: #fee2e2; color: #991b1b; }
.badge-info { background: #e0f2fe; color: #075985; }

/* Tables */
.table-container {
    overflow-x: auto;
}

table {
    width: 100%;
    border-collapse: collapse;
}

table th {
    background: var(--bg-main);
    padding: 12px;
    text-align: left;
    font-weight: 600;
    font-size: 14px;
    color: var(--text-secondary);
    border-bottom: 2px solid var(--border);
}

table td {
    padding: 12px;
    border-bottom: 1px solid var(--border);
    font-size: 14px;
}

table tr:last-child td {
    border-bottom: none;
}

table tr:hover {
    background: var(--bg-main);
}

/* Progress Bar */
.progress {
    height: 8px;
    background: var(--bg-main);
    border-radius: 4px;
    overflow: hidden;
    margin: 10px 0;
}

.progress-bar {
    height: 100%;
    background: var(--primary);
    transition: width 0.3s ease;
}

.progress-bar.success { background: var(--success); }
.progress-bar.warning { background: var(--warning); }
.progress-bar.danger { background: var(--danger); }

/* Forms */
.form-group {
    margin-bottom: 20px;
}

.form-label {
    display: block;
    margin-bottom: 8px;
    font-weight: 500;
    font-size: 14px;
    color: var(--text-primary);
}

.form-control {
    width: 100%;
    padding: 10px 14px;
    border: 1px solid var(--border);
    border-radius: 8px;
    font-size: 14px;
    transition: border 0.2s;
}

.form-control:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
}

select.form-control {
    cursor: pointer;
}

textarea.form-control {
    resize: vertical;
    min-height: 100px;
}

/* Radio and Checkbox */
.radio-group {
    display: flex;
    flex-direction: column;
    gap: 10px;
}

.radio-option {
    display: flex;
    align-items: center;
    padding: 12px;
    border: 2px solid var(--border);
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s;
}

.radio-option:hover {
    border-color: var(--primary);
    background: rgba(59, 130, 246, 0.02);
}

.radio-option input[type="radio"] {
    margin-right: 12px;
    width: 18px;
    height: 18px;
    cursor: pointer;
}

.radio-option.selected {
    border-color: var(--primary);
    background: rgba(59, 130, 246, 0.05);
}

/* Question Card */
.question-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 12px;
    padding: 24px;
    margin-bottom: 20px;
    box-shadow: var(--shadow);
}

.question-number {
    font-size: 14px;
    font-weight: 600;
    color: var(--primary);
    margin-bottom: 8px;
}

.question-text {
    font-size: 16px;
    font-weight: 500;
    color: var(--text-primary);
    margin-bottom: 16px;
    line-height: 1.6;
}

/* Alert Messages */
.alert {
    padding: 14px 18px;
    border-radius: 8px;
    margin-bottom: 20px;
    font-size: 14px;
    border-left: 4px solid;
}

.alert-success {
    background: #d1fae5;
    color: #065f46;
    border-color: var(--success);
}

.alert-danger {
    background: #fee2e2;
    color: #991b1b;
    border-color: var(--danger);
}

.alert-warning {
    background: #fef3c7;
    color: #92400e;
    border-color: var(--warning);
}

.alert-info {
    background: #e0f2fe;
    color: #075985;
    border-color: var(--info);
}

/* Timer */
.timer {
    position: fixed;
    top: 80px;
    right: 30px;
    background: white;
    padding: 16px 24px;
    border-radius: 12px;
    box-shadow: var(--shadow-lg);
    border: 2px solid var(--border);
    z-index: 999;
}

.timer-label {
    font-size: 12px;
    color: var(--text-secondary);
    margin-bottom: 4px;
}

.timer-value {
    font-size: 28px;
    font-weight: 700;
    color: var(--text-primary);
}

.timer-value.warning {
    color: var(--warning);
}

.timer-value.danger {
    color: var(--danger);
}

/* Leaderboard */
.rank-card {
    background: var(--bg-card);
    border: 2px solid var(--border);
    border-radius: 12px;
    padding: 16px;
    margin-bottom: 12px;
    display: flex;
    align-items: center;
    gap: 16px;
}

.rank-card.highlight {
    background: rgba(59, 130, 246, 0.05);
    border-color: var(--primary);
}

.rank-badge {
    width: 48px;
    height: 48px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 20px;
    font-weight: 700;
}

.rank-badge.gold { background: #fef3c7; color: #f59e0b; }
.rank-badge.silver { background: #e5e7eb; color: #6b7280; }
.rank-badge.bronze { background: #fed7aa; color: #c2410c; }
.rank-badge.default { background: var(--bg-main); color: var(--text-secondary); }

/* Footer */
.footer {
    background: var(--bg-card);
    border-top: 1px solid var(--border);
    padding: 20px 30px;
    text-align: center;
    color: var(--text-secondary);
    font-size: 14px;
}

/* Mobile Responsive */
@media (max-width: 768px) {
    .sidebar {
        transform: translateX(-100%);
    }
    
    .sidebar.active {
        transform: translateX(0);
    }
    
    .main-content {
        margin-left: 0;
    }
    
    .hamburger {
        display: flex;
    }
    
    .content {
        padding: 20px 15px;
    }
    
    .stats-grid {
        grid-template-columns: 1fr;
    }
    
    .page-title {
        font-size: 20px;
    }
    
    .header {
        padding: 0 15px;
    }
    
    .user-name {
        display: none;
    }
    
    .timer {
        top: 70px;
        right: 15px;
        padding: 12px 16px;
    }
    
    .timer-value {
        font-size: 20px;
    }
}

/* Auth Pages */
.auth-container {
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 100%);
    padding: 20px;
}

.auth-card {
    background: white;
    border-radius: 16px;
    box-shadow: var(--shadow-lg);
    padding: 40px;
    width: 100%;
    max-width: 440px;
}

.auth-logo {
    text-align: center;
    margin-bottom: 30px;
}

.auth-logo h1 {
    font-size: 32px;
    font-weight: 700;
    color: var(--primary);
}

.auth-title {
    font-size: 24px;
    font-weight: 700;
    text-align: center;
    margin-bottom: 8px;
    color: var(--text-primary);
}

.auth-subtitle {
    text-align: center;
    color: var(--text-secondary);
    margin-bottom: 30px;
    font-size: 14px;
}

.auth-footer {
    text-align: center;
    margin-top: 24px;
    font-size: 14px;
    color: var(--text-secondary);
}

.auth-footer a {
    color: var(--primary);
    text-decoration: none;
    font-weight: 600;
}

.auth-footer a:hover {
    text-decoration: underline;
}

/* Loading Spinner */
.spinner {
    border: 3px solid rgba(0, 0, 0, 0.1);
    border-left-color: var(--primary);
    border-radius: 50%;
    width: 40px;
    height: 40px;
    animation: spin 1s linear infinite;
    margin: 20px auto;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* Empty State */
.empty-state {
    text-align: center;
    padding: 60px 20px;
}

.empty-state svg {
    width: 80px;
    height: 80px;
    color: var(--text-light);
    margin-bottom: 16px;
}

.empty-state h3 {
    font-size: 18px;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 8px;
}

.empty-state p {
    color: var(--text-secondary);
    font-size: 14px;
}

/* Utility Classes */
.text-center { text-align: center; }
.text-right { text-align: right; }
.mb-10 { margin-bottom: 10px; }
.mb-20 { margin-bottom: 20px; }
.mb-30 { margin-bottom: 30px; }
.mt-20 { margin-top: 20px; }
.mt-30 { margin-top: 30px; }
.d-flex { display: flex; }
.justify-between { justify-content: space-between; }
.align-center { align-items: center; }
.gap-10 { gap: 10px; }
.gap-20 { gap: 20px; }
.w-100 { width: 100%; }