    <style>

        * {
            box-sizing: border-box;
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
        }
        
        body {
            margin: 0;
            padding: 0;
            background: #f5f7fa;
            color: #333;
        }
        
        .container {
            max-width: 1000px;
            margin: 0 auto;
            padding: 20px;
        }
        
        h1 {
            color: #2c3e50;
            text-align: center;
            margin-bottom: 30px;
        }
        
        .calculator-tabs {
            display: flex;
            margin-bottom: 20px;
            border-bottom: 1px solid #ddd;
        }
        
        .tab-btn {
            padding: 10px 20px;
            background: none;
            border: none;
            cursor: pointer;
            font-size: 16px;
            color: #7f8c8d;
            border-bottom: 3px solid transparent;
            transition: all 0.3s;
        }
        
        .tab-btn.active {
            color: #3498db;
            border-bottom: 3px solid #3498db;
            font-weight: bold;
        }
        
        .calculator-panel {
            display: none;
            background: white;
            padding: 25px;
            border-radius: 8px;
            box-shadow: 0 2px 10px rgba(0,0,0,0.1);
        }
        
        .calculator-panel.active {
            display: block;
        }
        
        .input-group {
            margin-bottom: 15px;
        }
        
        label {
            display: block;
            margin-bottom: 5px;
            font-weight: 500;
        }
        
        input, select {
            width: 100%;
            padding: 10px;
            border: 1px solid #ddd;
            border-radius: 4px;
            font-size: 16px;
        }
        
        button.calculate-btn {
            background: #3498db;
            color: white;
            border: none;
            padding: 12px 20px;
            border-radius: 4px;
            cursor: pointer;
            font-size: 16px;
            width: 100%;
            margin-top: 10px;
            transition: background 0.3s;
        }
        
        button.calculate-btn:hover {
            background: #2980b9;
        }
        
        .result-container {
            margin-top: 20px;
            padding: 15px;
            background: #f8f9fa;
            border-radius: 4px;
            display: none;
        }
        
        .result-item {
            display: flex;
            justify-content: space-between;
            margin-bottom: 8px;
        }
        
        .result-item .label {
            font-weight: 500;
        }
        
        .result-item .value {
            font-weight: bold;
            color: #2c3e50;
        }
        
        @media (max-width: 768px) {
            .calculator-tabs {
                flex-direction: column;
            }
            
            .tab-btn {
                text-align: left;
                border-bottom: none;
                border-left: 3px solid transparent;
            }
            
            .tab-btn.active {
                border-bottom: none;
                border-left: 3px solid #3498db;
            }
        }
    </style>