<title>Simple Calculator</title> <style> body { font-family: Arial, sans-serif; background-color: #f4f4f9; display: flex; justify-content: center; align-items: center; height: 100vh; margin: 0; }

    .calculator {
        background: #fff;
        padding: 20px;
        border-radius: 10px;
        box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
        width: 300px;
    }

    .display {
        width: 100%;
        height: 50px;
        background: #eee;
        border: none;
        border-radius: 5px;
        margin-bottom: 20px;
        font-size: 1.5rem;
        text-align: right;
        padding: 10px;
        box-sizing: border-box;
    }

    .buttons {
        display: grid;
        grid-template-columns: repeat(4, 1fr);
        gap: 10px;
    }

    .button {
        padding: 15px;
        font-size: 1.2rem;
        text-align: center;
        background: #4caf50;
        color: white;
        border: none;
        border-radius: 5px;
        cursor: pointer;
        transition: background 0.3s ease;
    }

    .button:hover {
        background: #45a049;
    }

    .button.operator {
        background: #2196f3;
    }

    .button.operator:hover {
        background: #1e88e5;
    }

    .button.clear {
        background: #f44336;
    }

    .button.clear:hover {
        background: #e53935;
    }

</style>

7 8 9 /

        <button class="button" onclick="appendNumber('4')">4</button>
        <button class="button" onclick="appendNumber('5')">5</button>
        <button class="button" onclick="appendNumber('6')">6</button>
        <button class="button operator" onclick="appendOperator('*')">*</button>

        <button class="button" onclick="appendNumber('1')">1</button>
        <button class="button" onclick="appendNumber('2')">2</button>
        <button class="button" onclick="appendNumber('3')">3</button>
        <button class="button operator" onclick="appendOperator('-')">-</button>

        <button class="button" onclick="appendNumber('0')">0</button>
        <button class="button" onclick="appendNumber('.')">.</button>
        <button class="button clear" onclick="clearDisplay()">C</button>
        <button class="button operator" onclick="appendOperator('+')">+</button>

        <button class="button operator" style="grid-column: span 4;" onclick="calculateResult()">=</button>
    </div>
</div>

<script>
    const display = document.getElementById('display');

    function appendNumber(number) {
        display.value += number;
    }

    function appendOperator(operator) {
        if (display.value !== '' && !isNaN(display.value.slice(-1))) {
            display.value += operator;
        }
    }

    function clearDisplay() {
        display.value = '';
    }

    function calculateResult() {
        try {
            display.value = eval(display.value);
        } catch {
            display.value = 'Error';
        }
    }
</script>