:root {
            --primary-color: #4a6fa5;
            --secondary-color: #166088;
            --accent-color: #e74c3c;
            --light-color: #f5f7fa;
            --dark-color: #2c3e50;
            --success-color: #2ecc71;
            --monday-color: #3498db;
            --tuesday-color: #9b59b6;
            --wednesday-color: #e67e22;
        }
        
        * {
            box-sizing: border-box;
            margin: 0;
            padding: 0;
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
        }
        
        body {
            background-color: #f0f4f8;
            color: #333;
            line-height: 1.6;
            padding: 20px;
        }
        
        .container {
            max-width: 900px;
            margin: 0 auto;
            background: white;
            border-radius: 10px;
            box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
            padding: 30px;
        }
        
        h1 {
            text-align: center;
            color: var(--primary-color);
            margin-bottom: 20px;
        }
        
        .description {
            text-align: center;
            margin-bottom: 30px;
            color: var(--dark-color);
        }
        
        .form-group {
            margin-bottom: 20px;
            position: relative;
        }
        
        label {
            display: block;
            margin-bottom: 8px;
            font-weight: 600;
            color: var(--secondary-color);
        }
        
        input[type="text"],
        input[type="email"],
        select {
            width: 100%;
            padding: 12px;
            border: 1px solid #ddd;
            border-radius: 5px;
            font-size: 16px;
            transition: border 0.3s;
        }
        
        input[type="text"]:focus,
        input[type="email"]:focus,
        select:focus {
            border-color: var(--primary-color);
            outline: none;
        }
        
        .error-input {
            border-color: var(--accent-color) !important;
        }
        
        .error-text {
            color: var(--accent-color);
            font-size: 14px;
            margin-top: 5px;
            display: none;
        }
        
        .day-section {
            margin-bottom: 30px;
            border-radius: 8px;
            padding: 20px;
        }
        
        .day-header {
            font-size: 20px;
            font-weight: 700;
            margin-bottom: 15px;
            padding-bottom: 10px;
            border-bottom: 2px solid;
        }
        
        .monday {
            background-color: rgba(52, 152, 219, 0.1);
            border-left: 5px solid var(--monday-color);
        }
        
        .monday .day-header {
            color: var(--monday-color);
            border-bottom-color: var(--monday-color);
        }
        
        .tuesday {
            background-color: rgba(155, 89, 182, 0.1);
            border-left: 5px solid var(--tuesday-color);
        }
        
        .tuesday .day-header {
            color: var(--tuesday-color);
            border-bottom-color: var(--tuesday-color);
        }
        
        .wednesday {
            background-color: rgba(230, 126, 34, 0.1);
            border-left: 5px solid var(--wednesday-color);
        }
        
        .wednesday .day-header {
            color: var(--wednesday-color);
            border-bottom-color: var(--wednesday-color);
        }
        
        .activity-option {
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding: 12px;
            border: 1px solid #ddd;
            border-radius: 5px;
            margin-bottom: 10px;
            transition: all 0.3s;
            background-color: white;
        }
        
        .activity-option:hover {
            background-color: #f9f9f9;
        }
        
        .activity-option input[type="radio"] {
            margin-right: 10px;
        }
        
        .activity-info {
            flex-grow: 1;
        }
        
        .activity-name {
            font-weight: 600;
            margin-bottom: 5px;
        }
        
        .activity-teacher {
            font-size: 14px;
            color: #666;
        }
        
        .activity-count {
            font-weight: bold;
            padding: 5px 10px;
            border-radius: 15px;
            background-color: #eee;
            min-width: 80px;
            text-align: center;
        }
        
        .full {
            background-color: var(--accent-color);
            color: white;
        }
        
        .almost-full {
            background-color: #f39c12;
            color: white;
        }
        
        .available {
            background-color: var(--success-color);
            color: white;
        }
        
        button {
            background-color: var(--primary-color);
            color: white;
            border: none;
            padding: 12px 20px;
            border-radius: 5px;
            cursor: pointer;
            font-size: 16px;
            font-weight: 600;
            width: 100%;
            transition: background-color 0.3s;
            margin-top: 20px;
        }
        
        button:hover {
            background-color: var(--secondary-color);
        }
        
        button:disabled {
            background-color: #ccc;
            cursor: not-allowed;
        }
        
        .message {
            padding: 15px;
            margin: 20px 0;
            border-radius: 5px;
            text-align: center;
            display: none;
        }
        
        .success {
            background-color: #d4edda;
            color: #155724;
            border: 1px solid #c3e6cb;
        }
        
        .error {
            background-color: #f8d7da;
            color: #721c24;
            border: 1px solid #f5c6cb;
        }
        
        .admin-link {
            text-align: center;
            margin-top: 20px;
        }
        
        .admin-link a {
            color: var(--primary-color);
            text-decoration: none;
        }
        
        .admin-link a:hover {
            text-decoration: underline;
        }
        
        @media (max-width: 600px) {
            .container {
                padding: 15px;
            }
            
            .activity-option {
                flex-direction: column;
                align-items: flex-start;
            }
            
            .activity-count {
                margin-top: 8px;
            }
        }