* {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            font-family: 'Arial', sans-serif;
        }
        
        body {
            display: flex;
            justify-content: center;
            align-items: center;
            min-height: 100vh;
            background: linear-gradient(135deg, #4b6cb7, #182848);
            padding: 20px;
        }
        
        .calculator {
            width: 300px;
            background-color: #1a1a1a;
            border-radius: 10px;
            box-shadow: 0 10px 20px rgba(0, 0, 0, 0.5);
            overflow: hidden;
        }
        
        .display {
            background-color: #000;
            color: white;
            padding: 20px;
            text-align: right;
            height: 100px;
            display: flex;
            flex-direction: column;
            justify-content: flex-end;
        }
        
        .previous-operation {
            color: rgba(255, 255, 255, 0.7);
            font-size: 1rem;
            min-height: 1.2rem;
            overflow: hidden;
            text-overflow: ellipsis;
            margin-bottom: 5px;
        }
        
        .current-value {
            font-size: 2.2rem;
            font-weight: 500;
            overflow: hidden;
            text-overflow: ellipsis;
        }
        
        .buttons {
            display: grid;
            grid-template-columns: repeat(4, 1fr);
            gap: 1px;
            background-color: #333;
        }
        
        button {
            border: none;
            outline: none;
            height: 60px;
            font-size: 1.5rem;
            cursor: pointer;
            transition: all 0.1s;
        }
        
        button:active {
            opacity: 0.8;
            transform: scale(0.98);
        }
        
        .gray-btn {
            background-color: #d4d4d2;
            color: #1a1a1a;
        }
        
        .gray-btn:active {
            background-color: #b8b8b6;
        }
        
        .dark-btn {
            background-color: #505050;
            color: white;
        }
        
        .dark-btn:active {
            background-color: #3d3d3d;
        }
        
        .orange-btn {
            background-color: #ff9500;
            color: white;
        }
        
        .orange-btn:active {
            background-color: #e08500;
        }
        
        .zero {
            grid-column: span 2;
        }