/* CSS remains exactly the same as before */
        :root {
            --primary-color: #3498db;
            --secondary-color: #2c3e50;
            --accent-color: #e74c3c;
            --light-color: #ecf0f1;
            --dark-color: #34495e;
        }

        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            margin: 0;
            padding: 0;
            background-color: #f5f7fa;
            color: #333;
        }

        /* ... rest of the CSS remains unchanged ... */
        .container {
            max-width: 1200px;
            margin: 0 auto;
            padding: 20px;
        }

        header {
            background-color: var(--secondary-color);
            color: white;
            padding: 15px 0;
            box-shadow: 0 2px 5px rgba(0,0,0,0.1);
        }

        .header-content {
            display: flex;
            justify-content: space-between;
            align-items: center;
        }

        h1 {
            margin: 0;
            font-size: 24px;
        }

        .class-selector {
            display: flex;
            gap: 10px;
            margin: 20px 0;
        }

        .class-btn {
            padding: 10px 20px;
            background-color: var(--light-color);
            border: none;
            border-radius: 4px;
            cursor: pointer;
            font-weight: bold;
            transition: all 0.3s;
        }

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

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

        .search-container {
            margin: 20px 0;
            display: flex;
            gap: 10px;
        }

        .search-input {
            flex: 1;
            padding: 10px;
            border: 1px solid #ddd;
            border-radius: 4px;
            font-size: 16px;
        }

        .btn {
            padding: 10px 20px;
            background-color: var(--primary-color);
            color: white;
            border: none;
            border-radius: 4px;
            cursor: pointer;
            font-size: 16px;
            transition: background-color 0.3s;
        }

        .btn:hover {
            background-color: #2980b9;
        }

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

        .btn-danger:hover {
            background-color: #c0392b;
        }

        .btn-success {
            background-color: #2ecc71;
        }

        .btn-success:hover {
            background-color: #27ae60;
        }

        .modal {
            display: none;
            position: fixed;
            z-index: 1000;
            left: 0;
            top: 0;
            width: 100%;
            height: 100%;
            background-color: rgba(0,0,0,0.5);
        }

        .modal-content {
            background-color: white;
            margin: 5% auto;
            padding: 20px;
            border-radius: 5px;
            width: 80%;
            max-width: 600px;
            box-shadow: 0 5px 15px rgba(0,0,0,0.3);
        }

        .modal-header {
            display: flex;
            justify-content: space-between;
            align-items: center;
            margin-bottom: 20px;
            padding-bottom: 10px;
            border-bottom: 1px solid #eee;
        }

        .close {
            font-size: 24px;
            cursor: pointer;
            color: #aaa;
        }

        .close:hover {
            color: #333;
        }

        .form-group {
            margin-bottom: 15px;
        }

        .form-group label {
            display: block;
            margin-bottom: 5px;
            font-weight: bold;
        }

        .form-control {
            width: 100%;
            padding: 8px;
            border: 1px solid #ddd;
            border-radius: 4px;
            font-size: 16px;
        }

        .form-actions {
            display: flex;
            justify-content: flex-end;
            gap: 10px;
            margin-top: 20px;
        }

        table {
            width: 100%;
            border-collapse: collapse;
            margin: 20px 0;
            box-shadow: 0 1px 3px rgba(0,0,0,0.1);
            background-color: white;
        }

        th, td {
            padding: 12px 15px;
            text-align: center;
            border-bottom: 1px solid #ddd;
        }

        th {
            background-color: var(--secondary-color);
            color: white;
            font-weight: bold;
        }

        tr:hover {
            background-color: #f5f5f5;
        }

        .action-btns {
            display: flex;
            gap: 5px;
            justify-content: center;
        }

        .action-btn {
            padding: 5px 10px;
            border: none;
            border-radius: 3px;
            cursor: pointer;
            color: white;
        }

        .edit-btn {
            background-color: #f39c12;
        }

        .edit-btn:hover {
            background-color: #e67e22;
        }

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

        .delete-btn:hover {
            background-color: #c0392b;
        }

        .chart-container {
            margin: 30px 0;
            background-color: white;
            padding: 20px;
            border-radius: 5px;
            box-shadow: 0 1px 3px rgba(0,0,0,0.1);
        }

        .chart-title {
            text-align: center;
            margin-bottom: 20px;
            color: var(--secondary-color);
        }

        .no-records {
            text-align: center;
            padding: 20px;
            background-color: white;
            border-radius: 5px;
            box-shadow: 0 1px 3px rgba(0,0,0,0.1);
        }

        @media (max-width: 768px) {
            .header-content {
                flex-direction: column;
                align-items: flex-start;
            }

            .class-selector {
                flex-direction: column;
            }

            .search-container {
                flex-direction: column;
            }

            table {
                display: block;
                overflow-x: auto;
            }
        }
        /* Modal styles */
        .modal {
            display: none;
            position: fixed;
            z-index: 1000;
            left: 0;
            top: 0;
            width: 100%;
            height: 100%;
            background-color: rgba(0,0,0,0.5);
            overflow: auto;
        }

        .modal-content {
            background-color: #fefefe;
            margin: 5% auto;
            padding: 20px;
            border: 1px solid #888;
            width: 80%;
            max-width: 700px;
            border-radius: 5px;
            box-shadow: 0 4px 8px rgba(0,0,0,0.1);
        }

        .modal-header {
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding-bottom: 10px;
            border-bottom: 1px solid #eee;
        }

        .modal-title {
            margin: 0;
            font-size: 1.5rem;
            color: #2c3e50;
        }

        .close {
            color: #aaa;
            font-size: 28px;
            font-weight: bold;
            cursor: pointer;
        }

        .close:hover {
            color: #333;
        }

        .form-row {
            display: flex;
            flex-wrap: wrap;
            margin: 0 -10px;
        }

        .form-col {
            flex: 1;
            min-width: 200px;
            padding: 0 10px;
            margin-bottom: 15px;
        }

        .form-actions {
            display: flex;
            justify-content: flex-end;
            gap: 10px;
            margin-top: 20px;
            padding-top: 15px;
            border-top: 1px solid #eee;
        }

        .form-control {
            width: 100%;
            padding: 8px;
            border: 1px solid #ddd;
            border-radius: 4px;
            font-size: 16px;
        }