:root {
    --bg-primary: #ffffff;
    --bg-secondary: #f8f9fa;
    --bg-gradient: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    --text-primary: #333333;
    --text-secondary: #666666;
    --border-color: #e1e5e9;
    --input-bg: #ffffff;
    --card-bg: #ffffff;
    --shadow: 0 15px 35px rgba(0, 0, 0, 0.1);
    --error-bg: #fee;
    --error-color: #c33;
    --error-border: #c33;
    --success-bg: #efe;
    --success-color: #3c3;
    --success-border: #3c3;
}

[data-theme="dark"] {
    --bg-primary: #1a1a1a;
    --bg-secondary: #2d2d2d;
    --bg-gradient: linear-gradient(135deg, #2d3748 0%, #4a5568 100%);
    --text-primary: #ffffff;
    --text-secondary: #a0aec0;
    --border-color: #4a5568;
    --input-bg: #2d3748;
    --card-bg: #2d3748;
    --shadow: 0 15px 35px rgba(0, 0, 0, 0.3);
    --error-bg: #742a2a;
    --error-color: #feb2b2;
    --error-border: #e53e3e;
    --success-bg: #2f855a;
    --success-color: #9ae6b4;
    --success-border: #38a169;
}

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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: var(--bg-gradient);
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--text-primary);
    transition: all 0.3s ease;
}

.container {
    background: var(--card-bg);
    padding: 2rem;
    border-radius: 15px;
    box-shadow: var(--shadow);
    width: 100%;
    max-width: 500px;
    margin: 1rem;
    transition: all 0.3s ease;
}

.theme-toggle {
    position: fixed;
    top: 20px;
    right: 20px;
    background: var(--card-bg);
    border: 2px solid var(--border-color);
    border-radius: 50px;
    padding: 8px 16px;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 14px;
    transition: all 0.3s ease;
    z-index: 1000;
}

.theme-toggle:hover {
    transform: scale(1.05);
}

.auth-header {
    text-align: center;
    margin-bottom: 2rem;
}

.auth-header h1 {
    color: var(--text-primary);
    font-size: 2rem;
    margin-bottom: 0.5rem;
}

.auth-header p {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.form-group {
    margin-bottom: 1.5rem;
}

.form-row {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
}

.form-group label {
    display: block;
    margin-bottom: 0.5rem;
    color: var(--text-primary);
    font-weight: 500;
}

.form-group input,
.form-group select,
.form-group textarea {
    width: 100%;
    padding: 0.75rem;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    font-size: 1rem;
    background: var(--input-bg);
    color: var(--text-primary);
    transition: border-color 0.3s ease;
}

.form-group input:focus,
.form-group select:focus,
.form-group textarea:focus {
    outline: none;
    border-color: #667eea;
}

.form-group textarea {
    resize: vertical;
    min-height: 80px;
}

.btn {
    width: 100%;
    padding: 0.75rem;
    background: var(--bg-gradient);
    color: white;
    border: none;
    border-radius: 8px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: transform 0.2s ease;
}

.btn:hover {
    transform: translateY(-2px);
}

.btn:disabled {
    opacity: 0.6;
    cursor: not-allowed;
    transform: none;
}

.btn-secondary {
    background: var(--bg-secondary);
    color: var(--text-primary);
    border: 2px solid var(--border-color);
    width: auto;
    padding: 0.5rem 1rem;
    font-size: 0.9rem;
}

.btn-secondary:hover {
    background: var(--border-color);
    transform: translateY(-1px);
}

.auth-switch {
    text-align: center;
    margin-top: 1.5rem;
    padding-top: 1.5rem;
    border-top: 1px solid var(--border-color);
}

.auth-switch a {
    color: #667eea;
    text-decoration: none;
    font-weight: 500;
}

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

.error-message {
    background: var(--error-bg);
    color: var(--error-color);
    padding: 0.75rem;
    border-radius: 8px;
    margin-bottom: 1rem;
    border-left: 4px solid var(--error-border);
}

.success-message {
    background: var(--success-bg);
    color: var(--success-color);
    padding: 0.75rem;
    border-radius: 8px;
    margin-bottom: 1rem;
    border-left: 4px solid var(--success-border);
}

.loading {
    display: inline-block;
    width: 20px;
    height: 20px;
    border: 3px solid #f3f3f3;
    border-top: 3px solid #667eea;
    border-radius: 50%;
    animation: spin 1s linear infinite;
}

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

.dashboard {
    max-width: 1000px;
    margin: 2rem auto;
    padding: 2rem;
    background: var(--card-bg);
    border-radius: 15px;
    box-shadow: var(--shadow);
}

.dashboard-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem;
    padding-bottom: 1rem;
    border-bottom: 1px solid var(--border-color);
}

.dashboard-nav {
    display: flex;
    gap: 1rem;
    margin-bottom: 2rem;
}

.nav-btn {
    padding: 0.5rem 1rem;
    background: var(--bg-secondary);
    color: var(--text-primary);
    border: 2px solid var(--border-color);
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.3s ease;
}

.nav-btn.active {
    background: var(--bg-gradient);
    color: white;
    border-color: transparent;
}

.nav-btn:hover {
    transform: translateY(-2px);
}

.profile-section {
    display: none;
}

.profile-section.active {
    display: block;
}

.profile-card {
    background: var(--bg-secondary);
    padding: 2rem;
    border-radius: 12px;
    margin-bottom: 2rem;
}

.profile-header {
    display: flex;
    align-items: center;
    gap: 2rem;
    margin-bottom: 2rem;
}

.profile-avatar {
    width: 100px;
    height: 100px;
    border-radius: 50%;
    background: var(--bg-gradient);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2rem;
    color: white;
    font-weight: bold;
}

.profile-info h2 {
    margin-bottom: 0.5rem;
    color: var(--text-primary);
}

.profile-info p {
    color: var(--text-secondary);
}

.info-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1rem;
}

.info-item {
    background: var(--card-bg);
    padding: 1rem;
    border-radius: 8px;
    border: 1px solid var(--border-color);
}

.info-item label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.info-item span {
    display: block;
    font-size: 1rem;
    color: var(--text-primary);
    font-weight: 500;
    margin-top: 0.25rem;
}

.logout-btn {
    background: #dc3545;
    color: white;
    border: none;
    padding: 0.5rem 1rem;
    border-radius: 5px;
    cursor: pointer;
}

.logout-btn:hover {
    background: #c82333;
}

.subjects-list {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
}

.subject-tag {
    background: var(--bg-gradient);
    color: white;
    padding: 0.25rem 0.75rem;
    border-radius: 20px;
    font-size: 0.85rem;
}

@media (max-width: 768px) {
    .container {
        margin: 0.5rem;
        padding: 1.5rem;
        max-width: none;
    }
    
    .dashboard {
        margin: 1rem;
        padding: 1.5rem;
    }

    .form-row {
        grid-template-columns: 1fr;
    }

    .dashboard-header {
        flex-direction: column;
        gap: 1rem;
        align-items: stretch;
    }

    .dashboard-nav {
        flex-wrap: wrap;
    }

    .profile-header {
        flex-direction: column;
        text-align: center;
    }

    .info-grid {
        grid-template-columns: 1fr;
    }

    .profile-card > div:first-child {
        flex-direction: column;
        align-items: stretch !important;
    }

    .profile-card > div:first-child > div {
        margin-top: 1rem;
        justify-content: center;
    }
}