body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            margin: 0;
            padding: 20px;
            background-color: #f0f4f8;
            color: #333;
        }
        .container {
            max-width: 500px;
            margin: 0 auto;
            background-color: #ffffff;
            border-radius: 12px;
            box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
            padding: 30px;
        }
        h1 {
            text-align: center;
            color: #2c3e50;
            margin-bottom: 30px;
        }
        .display {
            width: 100%;
            height: 60px;
            font-size: 20px;
            text-align: right;
            margin-bottom: 20px;
            padding: 10px;
            box-sizing: border-box;
            border: 2px solid #3498db;
            border-radius: 6px;
            background-color: #f8f9fa;
        }
        .calculator-grid {
            display: grid;
            grid-template-columns: repeat(5, 1fr);
            gap: 10px;
            margin-bottom: 20px;
        }
        button {
            padding: 15px;
            font-size: 14px;
            border: none;
            background-color: #ecf0f1;
            color: #2c3e50;
            cursor: pointer;
            transition: background-color 0.3s, transform 0.1s;
            border-radius: 6px;
            font-weight: 500;
        }
        button:hover {
            background-color: #d0d3d4;
        }
        button:active {
            transform: scale(0.95);
        }
        .operator {
            background-color: #3498db;
            color: white;
        }
        .operator:hover {
            background-color: #2980b9;
        }
        .scientific {
            background-color: #e74c3c;
            color: white;
        }
        .scientific:hover {
            background-color: #c0392b;
        }
        .equals {
            background-color: #2ecc71;
            color: white;
        }
        .equals:hover {
            background-color: #27ae60;
        }
        .memory {
            background-color: #9b59b6;
            color: white;
        }
        .memory:hover {
            background-color: #8e44ad;
        }
        .mode-switch {
            display: flex;
            justify-content: center;
            margin-bottom: 20px;
        }
        .mode-btn {
            padding: 10px 20px;
            margin: 0 5px;
            border: none;
            background-color: #95a5a6;
            color: white;
            cursor: pointer;
            border-radius: 6px;
        }
        .mode-btn.active {
            background-color: #3498db;
        }
        .history {
            margin-top: 20px;
            padding: 15px;
            background-color: #f8f9fa;
            border-radius: 6px;
            max-height: 200px;
            overflow-y: auto;
        }
        .history h3 {
            margin-top: 0;
            color: #2c3e50;
        }
        .history-item {
            padding: 5px 0;
            border-bottom: 1px solid #ddd;
            font-family: monospace;
        }
        .back-link {
            display: inline-block;
            margin-bottom: 20px;
            color: #3498db;
            text-decoration: none;
            transition: color 0.3s;
        }
        .back-link:hover {
            color: #2980b9;
        }

        /* Cross-linking styles */
        .cross-links-section {
            max-width: 1000px;
            margin: 40px auto 20px;
            background-color: #ffffff;
            border-radius: 12px;
            box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
            padding: 30px;
        }
        
        .cross-links-section h2 {
            text-align: center;
            color: #2c3e50;
            margin-bottom: 30px;
            font-size: 1.8em;
            border-bottom: 3px solid #3498db;
            padding-bottom: 15px;
        }
        
        .cross-link-category {
            margin-bottom: 30px;
        }
        
        .cross-link-category h3 {
            color: #2c3e50;
            margin-bottom: 15px;
            font-size: 1.3em;
            padding-left: 10px;
            border-left: 4px solid #3498db;
        }
        
        .cross-link-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
            gap: 15px;
        }
        
        .cross-link-card {
            display: block;
            text-decoration: none;
            color: #34495e;
            background: #f8f9fa;
            border: 2px solid #e9ecef;
            border-radius: 8px;
            padding: 15px;
            transition: all 0.3s ease;
            position: relative;
            overflow: hidden;
        }
        
        .cross-link-card:hover {
            transform: translateY(-3px);
            box-shadow: 0 6px 20px rgba(52, 152, 219, 0.15);
            border-color: #3498db;
            background: #e3f2fd;
            color: #2c3e50;
        }
        
        .cross-link-card span {
            font-weight: 500;
            display: block;
            line-height: 1.4;
        }
        
        .cross-link-card::before {
            content: '';
            position: absolute;
            top: 0;
            left: 0;
            width: 4px;
            height: 100%;
            background: #3498db;
            transform: scaleY(0);
            transition: transform 0.3s ease;
        }
        
        .cross-link-card:hover::before {
            transform: scaleY(1);
        }
        
        @media (max-width: 768px) {
            .cross-links-section {
                margin: 20px;
                padding: 20px;
            }
            
            .cross-link-grid {
                grid-template-columns: 1fr;
                gap: 12px;
            }
            
            .cross-link-card {
                padding: 12px;
            }
        }