body {
            font-family: 'Helvetica Neue', sans-serif;
            background-color: #000;
            color: #fff;
            margin: 0;
            display: flex;
            justify-content: center;
            align-items: center;
            height: 100vh;
        }

        .calculator {
            width: 320px;
            padding: 20px;
            border-radius: 30px;
            box-shadow: 0 0 15px rgba(0, 0, 0, 0.2);
            background-color: #333;
        }

        #display {
            width: 87%;
            height: 80px;
            font-size: 36px;
            text-align: right;
            padding: 20px;
            margin-bottom: 20px;
            border: none;
            border-radius: 20px;
            background-color: #000;
            color: #fff;
            box-shadow: inset 0 0 5px rgba(0, 0, 0, 0.5);
        }

        .buttons {
            display: grid;
            grid-template-columns: repeat(4, 1fr);
            gap: 15px;
        }

        button {
            height: 60px;
            font-size: 28px;
            border: none;
            border-radius: 30px;
            cursor: pointer;
            transition: background-color 0.3s ease;
        }

        /* Digit buttons (1-9) */
        button:not(.operator):not(#zero):not(#clear):not(#backspace):not(#equals) {
            background-color: #505050;
            color: #fff;
        }

        /* Zero button */
        #zero {
            grid-column: span 2;
            background-color: #505050;
            color: #fff;
        }

        /* Operator buttons (+, -, ×, ÷, =) */
        .operator {
            background-color: #ff9500;
            color: #fff;
        }

        /* Clear and backspace buttons */
        #clear, #backspace {
            background-color: #d4d4d2;
            color: #000;
        }

        button:hover {
            opacity: 0.9;
        }