/* Root Variables for Light/Dark Theme */
:root {
    --bg-primary: #ffffff;
    --bg-secondary: #f8fafc;
    --bg-tertiary: #f1f5f9;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --text-tertiary: #94a3b8;
    --accent: #6366f1;
    --accent-hover: #4f46e5;
    --accent-light: #eef2ff;
    --border: #e2e8f0;
    --border-light: #f1f5f9;
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
    --success: #10b981;
    --success-light: #d1fae5;
    --danger: #ef4444;
    --danger-light: #fee2e2;
    --warning: #f59e0b;
    --warning-light: #fef3c7;
    --radius-sm: 8px;
    --radius: 12px;
    --radius-lg: 16px;
}

[data-theme="dark"] {
    --bg-primary: #0f172a;
    --bg-secondary: #1e293b;
    --bg-tertiary: #334155;
    --text-primary: #f1f5f9;
    --text-secondary: #cbd5e1;
    --text-tertiary: #94a3b8;
    --accent: #818cf8;
    --accent-hover: #6366f1;
    --accent-light: #312e81;
    --border: #334155;
    --border-light: #1e293b;
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.3);
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.3);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.3);
    --success-light: #064e3b;
    --danger-light: #7f1d1d;
    --warning-light: #78350f;
}

/* Reset & Base */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen', 'Ubuntu', 'Cantarell', sans-serif;
    background: var(--bg-secondary);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* Home Page Styles */
.home-container {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 24px;
    background: linear-gradient(135deg, var(--accent-light) 0%, var(--bg-secondary) 100%);
}

.home-title {
    font-size: 28px;
    font-weight: 800;
    text-align: center;
    margin-bottom: 16px;
    color: var(--accent);
    letter-spacing: -0.5px;
}

.home-subtitle {
    font-size: 16px;
    color: var(--text-secondary);
    text-align: center;
    margin-bottom: 48px;
}

.home-buttons {
    display: flex;
    flex-direction: column;
    gap: 16px;
    width: 100%;
    max-width: 400px;
    margin-bottom: 32px;
}

.share-section {
    margin-bottom: 32px;
}

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

.auth-card {
    width: 100%;
    max-width: 440px;
    background: var(--bg-primary);
    border-radius: var(--radius-lg);
    padding: 32px 24px;
    box-shadow: var(--shadow-xl);
}

.auth-header {
    text-align: center;
    margin-bottom: 32px;
}

.auth-header h1 {
    font-size: 24px;
    font-weight: 800;
    color: var(--text-primary);
    margin-bottom: 8px;
    letter-spacing: -0.5px;
}

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

.auth-form {
    width: 100%;
}

.auth-links {
    text-align: center;
    margin-top: 16px;
}

.auth-links a {
    color: var(--accent);
    text-decoration: none;
    font-size: 14px;
    font-weight: 600;
}

.auth-footer {
    text-align: center;
    margin-top: 24px;
    padding-top: 24px;
    border-top: 1px solid var(--border);
    color: var(--text-secondary);
    font-size: 14px;
}

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

.back-home {
    text-align: center;
    margin-top: 24px;
}

.back-home a {
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 14px;
    transition: color 0.2s;
}

.back-home a:hover {
    color: var(--accent);
}

/* Class Selection */
.class-selection {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.class-card {
    width: 100%;
    background: var(--bg-secondary);
    border: 2px solid var(--border);
    border-radius: var(--radius);
    padding: 16px;
    text-align: left;
    cursor: pointer;
    transition: all 0.2s;
    font-family: inherit;
}

.class-card:hover {
    border-color: var(--accent);
    background: var(--accent-light);
    transform: translateY(-2px);
    box-shadow: var(--shadow);
}

.class-subject {
    font-size: 18px;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 4px;
}

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

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

.form-group label {
    display: block;
    margin-bottom: 8px;
    font-weight: 600;
    color: var(--text-primary);
    font-size: 14px;
}

.form-control {
    width: 100%;
    padding: 12px 16px;
    border: 2px solid var(--border);
    border-radius: var(--radius-sm);
    font-size: 16px;
    background: var(--bg-primary);
    color: var(--text-primary);
    transition: all 0.2s;
    font-family: inherit;
}

.form-control:focus {
    outline: none;
    border-color: var(--accent);
    box-shadow: 0 0 0 3px var(--accent-light);
}

.form-control::placeholder {
    color: var(--text-tertiary);
}

select.form-control {
    cursor: pointer;
    appearance: none;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' fill='%2364748b' viewBox='0 0 16 16'%3E%3Cpath d='M8 11L3 6h10z'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 12px center;
    padding-right: 40px;
}

.form-help {
    display: block;
    margin-top: 6px;
    font-size: 13px;
    color: var(--text-tertiary);
}

/* Buttons */
.btn {
    padding: 12px 24px;
    border: none;
    border-radius: var(--radius-sm);
    font-size: 16px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
    text-decoration: none;
    display: inline-block;
    text-align: center;
    font-family: inherit;
    user-select: none;
}

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

.btn-primary:hover {
    background: var(--accent-hover);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.btn-primary:active {
    transform: translateY(0);
}

.btn-secondary {
    background: var(--bg-primary);
    color: var(--text-primary);
    border: 2px solid var(--border);
}

.btn-secondary:hover {
    border-color: var(--accent);
    color: var(--accent);
    box-shadow: var(--shadow);
}

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

.btn-success:hover {
    background: #059669;
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

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

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

.btn-block {
    width: 100%;
    display: block;
}

.btn-lg {
    padding: 14px 28px;
    font-size: 17px;
}

/* Header */
header {
    background: var(--bg-primary);
    padding: 16px 20px;
    box-shadow: var(--shadow);
    position: sticky;
    top: 0;
    z-index: 100;
    border-bottom: 1px solid var(--border);
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    max-width: 1200px;
    margin: 0 auto;
}

.logo {
    font-size: 20px;
    font-weight: 800;
    color: var(--accent);
    letter-spacing: -0.5px;
}

/* Mobile Navigation */
.nav-links {
    display: flex;
    gap: 8px;
    list-style: none;
    flex-wrap: wrap;
}

.nav-links a {
    color: var(--text-secondary);
    text-decoration: none;
    font-weight: 600;
    font-size: 14px;
    padding: 8px 12px;
    border-radius: var(--radius-sm);
    transition: all 0.2s;
}

.nav-links a:hover,
.nav-links a.active {
    color: var(--accent);
    background: var(--accent-light);
}

/* Container */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px;
}

.mobile-container {
    max-width: 500px;
    margin: 0 auto;
    padding: 20px;
}

/* Cards */
.card {
    background: var(--bg-primary);
    border-radius: var(--radius);
    padding: 24px;
    box-shadow: var(--shadow);
    margin-bottom: 20px;
    border: 1px solid var(--border-light);
}

.card-title {
    font-size: 20px;
    font-weight: 700;
    margin-bottom: 16px;
    color: var(--text-primary);
    letter-spacing: -0.3px;
}

/* Dashboard Grid */
.dashboard-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
    gap: 16px;
    margin-top: 20px;
}

.stat-card {
    background: var(--bg-primary);
    padding: 20px;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    text-align: center;
    border: 1px solid var(--border-light);
    transition: all 0.2s;
}

.stat-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
}

.stat-number {
    font-size: 32px;
    font-weight: 800;
    color: var(--accent);
    margin-bottom: 4px;
    letter-spacing: -1px;
}

.stat-label {
    font-size: 12px;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.5px;
    font-weight: 600;
}

/* Tables */
.table-container {
    overflow-x: auto;
    margin-top: 16px;
    border-radius: var(--radius-sm);
    border: 1px solid var(--border);
}

table {
    width: 100%;
    border-collapse: collapse;
    background: var(--bg-primary);
}

thead {
    background: var(--accent);
    color: white;
}

th {
    padding: 14px 12px;
    text-align: left;
    font-weight: 600;
    font-size: 14px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

td {
    padding: 14px 12px;
    font-size: 15px;
}

tbody tr {
    border-bottom: 1px solid var(--border);
}

tbody tr:last-child {
    border-bottom: none;
}

tbody tr:hover {
    background: var(--bg-secondary);
}

/* Attendance Toggle */
.attendance-toggle {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 16px;
    background: var(--bg-secondary);
    border-radius: var(--radius-sm);
    margin-bottom: 12px;
    border: 2px solid var(--border-light);
    transition: all 0.2s;
}

.attendance-toggle:hover {
    border-color: var(--border);
    box-shadow: var(--shadow-sm);
}

.toggle-switch {
    position: relative;
    width: 56px;
    height: 32px;
}

.toggle-switch input {
    opacity: 0;
    width: 0;
    height: 0;
}

.toggle-slider {
    position: absolute;
    cursor: pointer;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: var(--danger);
    transition: 0.3s;
    border-radius: 32px;
}

.toggle-slider:before {
    position: absolute;
    content: "";
    height: 24px;
    width: 24px;
    left: 4px;
    bottom: 4px;
    background-color: white;
    transition: 0.3s;
    border-radius: 50%;
    box-shadow: var(--shadow-sm);
}

input:checked + .toggle-slider {
    background-color: var(--success);
}

input:checked + .toggle-slider:before {
    transform: translateX(24px);
}

/* Theme Toggle */
.theme-toggle {
    background: var(--bg-secondary);
    border: 2px solid var(--border);
    border-radius: 50%;
    width: 44px;
    height: 44px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 20px;
    transition: all 0.3s;
}

.theme-toggle:hover {
    transform: scale(1.1) rotate(180deg);
    border-color: var(--accent);
}

/* Alerts */
.alert {
    padding: 14px 16px;
    border-radius: var(--radius-sm);
    margin-bottom: 20px;
    font-size: 15px;
    line-height: 1.5;
}

.alert-success {
    background: var(--success-light);
    color: #065f46;
    border: 1px solid var(--success);
}

[data-theme="dark"] .alert-success {
    color: #d1fae5;
}

.alert-error {
    background: var(--danger-light);
    color: #991b1b;
    border: 1px solid var(--danger);
}

[data-theme="dark"] .alert-error {
    color: #fecaca;
}

.alert-info {
    background: #dbeafe;
    color: #1e40af;
    border: 1px solid #3b82f6;
}

[data-theme="dark"] .alert-info {
    background: #1e3a8a;
    color: #bfdbfe;
}

/* Loading Spinner */
.spinner {
    border: 3px solid var(--border);
    border-top: 3px solid var(--accent);
    border-radius: 50%;
    width: 40px;
    height: 40px;
    animation: spin 1s linear infinite;
    margin: 20px auto;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

/* Utility Classes */
.text-center {
    text-align: center;
}

.mt-20 {
    margin-top: 20px;
}

.mb-20 {
    margin-bottom: 20px;
}

.hidden {
    display: none;
}

/* Responsive Design */
@media (max-width: 640px) {
    .home-title {
        font-size: 24px;
    }
    
    .auth-card {
        padding: 28px 20px;
    }
    
    .nav-links {
        font-size: 12px;
    }
    
    .nav-links a {
        padding: 6px 10px;
    }
    
    .dashboard-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: 12px;
    }
    
    .stat-card {
        padding: 16px;
    }
    
    .stat-number {
        font-size: 28px;
    }
    
    table {
        font-size: 13px;
    }
    
    th, td {
        padding: 10px 8px;
    }
}

@media (min-width: 768px) {
    .dashboard-grid {
        grid-template-columns: repeat(3, 1fr);
    }
}