:root {
            --primary-color: #667eea;
            --primary-dark: #5568d3;
            --secondary-color: #764ba2;
            --success-color: #48bb78;
            --error-color: #f56565;
            --bg-light: #f7fafc;
            --bg-dark: #1a202c;
            --text-light: #2d3748;
            --text-dark: #e2e8f0;
            --border-light: #e2e8f0;
            --border-dark: #4a5568;
            --card-light: #ffffff;
            --card-dark: #2d3748;
        }
        
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }
        
        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            line-height: 1.6;
            background: var(--bg-light);
            color: var(--text-light);
            min-height: 100vh;
            display: flex;
            align-items: center;
            justify-content: center;
            padding: 1rem;
        }
        
        body.dark-mode {
            background: var(--bg-dark);
            color: var(--text-dark);
        }
        
        .container {
            max-width: 500px;
            width: 100%;
        }
        
        .card {
            background: var(--card-light);
            border-radius: 12px;
            padding: 2rem;
            box-shadow: 0 4px 6px rgba(0,0,0,0.1);
        }
        
        body.dark-mode .card {
            background: var(--card-dark);
        }
        
        .card h1 {
            margin-bottom: 0.5rem;
            color: var(--primary-color);
            text-align: center;
        }
        
        .card p {
            margin-bottom: 1.5rem;
            text-align: center;
            color: #718096;
        }
        
        .form-group {
            margin-bottom: 1.5rem;
        }
        
        .form-group label {
            display: block;
            margin-bottom: 0.5rem;
            font-weight: 600;
        }
        
        .form-group input {
            width: 100%;
            padding: 0.75rem;
            border: 2px solid var(--border-light);
            border-radius: 8px;
            font-size: 1rem;
            transition: border-color 0.3s;
        }
        
        body.dark-mode .form-group input {
            background: var(--bg-dark);
            border-color: var(--border-dark);
            color: var(--text-dark);
        }
        
        .form-group input:focus {
            outline: none;
            border-color: var(--primary-color);
        }
        
        .btn {
            width: 100%;
            background: linear-gradient(135deg, var(--primary-color) 0%, var(--secondary-color) 100%);
            color: white;
            padding: 0.75rem 2rem;
            border: none;
            border-radius: 8px;
            font-size: 1rem;
            font-weight: 600;
            cursor: pointer;
            transition: transform 0.2s, box-shadow 0.2s;
        }
        
        .btn:hover {
            transform: translateY(-2px);
            box-shadow: 0 4px 12px rgba(102, 126, 234, 0.4);
        }
        
        .btn:active {
            transform: translateY(0);
        }
        
        .alert {
            padding: 1rem;
            border-radius: 8px;
            margin-bottom: 1.5rem;
        }
        
        .alert-error {
            background: #fed7d7;
            color: #742a2a;
            border: 1px solid #fc8181;
        }
        
        .alert-success {
            background: #c6f6d5;
            color: #22543d;
            border: 1px solid #68d391;
        }
        
        .back-link {
            text-align: center;
            margin-top: 1.5rem;
        }
        
        .back-link a {
            color: var(--primary-color);
            text-decoration: none;
        }
        
        .back-link a:hover {
            text-decoration: underline;
        }
        
        .theme-toggle {
            position: fixed;
            top: 1rem;
            right: 1rem;
            background: rgba(102, 126, 234, 0.2);
            border: none;
            color: var(--primary-color);
            padding: 0.5rem 1rem;
            border-radius: 20px;
            cursor: pointer;
            font-size: 0.9rem;
            transition: background 0.3s;
        }
        
        .theme-toggle:hover {
            background: rgba(102, 126, 234, 0.3);
        }