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

        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            min-height: 100vh;
            padding: 20px;
        }

        .container {
            max-width: 1200px;
            margin: 0 auto;
            background: white;
            border-radius: 20px;
            box-shadow: 0 20px 40px rgba(0,0,0,0.1);
            overflow: hidden;
        }

        .header {
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            color: white;
            padding: 30px;
            text-align: center;
        }

        .header h1 {
            font-size: 2.5em;
            margin-bottom: 10px;
        }

        .header p {
            font-size: 1.2em;
            opacity: 0.9;
        }

        .nav {
            background: #f8f9fa;
            padding: 15px 30px;
            border-bottom: 1px solid #e9ecef;
        }

        .nav a {
            color: #667eea;
            text-decoration: none;
            margin-right: 20px;
            font-weight: 500;
        }

        .nav a:hover {
            text-decoration: underline;
        }

        .back-link {
            display: inline-block;
            margin-top: 20px;
            color: #667eea;
            text-decoration: none;
            font-weight: 500;
        }

        .back-link:hover {
            text-decoration: underline;
        }

        .content {
            padding: 30px;
        }

        .calculator-section {
            margin-bottom: 40px;
            padding: 25px;
            border: 1px solid #e9ecef;
            border-radius: 15px;
            background: #f8f9fa;
        }

        .calculator-section h2 {
            color: #333;
            margin-bottom: 20px;
            font-size: 1.5em;
            border-bottom: 2px solid #667eea;
            padding-bottom: 10px;
        }

        .input-group {
            margin-bottom: 20px;
        }

        .input-group label {
            display: block;
            margin-bottom: 8px;
            font-weight: 600;
            color: #333;
        }

        .input-group input, .input-group select {
            width: 100%;
            padding: 12px;
            border: 2px solid #ddd;
            border-radius: 8px;
            font-size: 16px;
            transition: border-color 0.3s;
        }

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

        .button-group {
            display: flex;
            gap: 10px;
            flex-wrap: wrap;
        }

        .btn {
            padding: 12px 24px;
            border: none;
            border-radius: 8px;
            font-size: 16px;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.3s;
            flex: 1;
            min-width: 120px;
        }

        .btn-primary {
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            color: white;
        }

        .btn-primary:hover {
            transform: translateY(-2px);
            box-shadow: 0 5px 15px rgba(102, 126, 234, 0.4);
        }

        .btn-secondary {
            background: #6c757d;
            color: white;
        }

        .btn-secondary:hover {
            background: #5a6268;
        }

        .result {
            margin-top: 20px;
            padding: 20px;
            background: white;
            border-radius: 10px;
            border-left: 4px solid #667eea;
            display: none;
        }

        .result.show {
            display: block;
        }

        .result h3 {
            color: #333;
            margin-bottom: 15px;
        }

        .result-value {
            font-size: 1.5em;
            font-weight: bold;
            color: #667eea;
            margin: 10px 0;
        }

        .rectangle-display {
            background: #f8f9fa;
            padding: 20px;
            border-radius: 10px;
            text-align: center;
            margin: 15px 0;
        }

        .rectangle {
            width: 200px;
            height: 120px;
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            margin: 20px auto;
            border-radius: 10px;
            position: relative;
            display: flex;
            align-items: center;
            justify-content: center;
            color: white;
            font-weight: bold;
            box-shadow: 0 5px 15px rgba(0,0,0,0.2);
        }

        .rectangle::before {
            content: '';
            position: absolute;
            top: 0;
            left: 0;
            right: 0;
            bottom: 0;
            border: 2px solid rgba(255,255,255,0.3);
            border-radius: 10px;
        }

        .dimensions {
            position: absolute;
            background: rgba(255,255,255,0.9);
            color: #333;
            padding: 5px 10px;
            border-radius: 5px;
            font-size: 0.9em;
            font-weight: bold;
        }

        .width-label {
            bottom: -30px;
            left: 50%;
            transform: translateX(-50%);
        }

        .height-label {
            right: -40px;
            top: 50%;
            transform: translateY(-50%);
        }

        .diagonal {
            position: absolute;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            border-top: 2px dashed rgba(255,255,255,0.7);
            transform-origin: 0 0;
        }

        .formula {
            background: #e9ecef;
            padding: 15px;
            border-radius: 8px;
            font-family: 'Courier New', monospace;
            margin: 15px 0;
            border-left: 4px solid #667eea;
        }

        .error {
            color: #dc3545;
            background: #f8d7da;
            padding: 10px;
            border-radius: 5px;
            margin: 10px 0;
            display: none;
        }

        .info-box {
            background: #d1ecf1;
            border: 1px solid #bee5eb;
            color: #0c5460;
            padding: 15px;
            border-radius: 8px;
            margin: 15px 0;
        }

        .metrics-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
            gap: 15px;
            margin: 15px 0;
        }

        .metric-card {
            background: white;
            padding: 20px;
            border-radius: 10px;
            text-align: center;
            border-left: 4px solid #28a745;
            box-shadow: 0 2px 10px rgba(0,0,0,0.1);
        }

        .metric-value {
            font-size: 2em;
            font-weight: bold;
            color: #28a745;
            margin-bottom: 5px;
        }

        .metric-label {
            color: #666;
            font-size: 0.9em;
        }

        @media (max-width: 768px) {
            .header h1 {
                font-size: 2em;
            }
            
            .content {
                padding: 20px;
            }
            
            .button-group {
                flex-direction: column;
            }
            
            .btn {
                flex: none;
            }
            
            .rectangle {
                width: 150px;
                height: 90px;
            }
            
            .metrics-grid {
                grid-template-columns: 1fr;
            }
        }

        /* 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;
            }
        }