<html>
<body>
<h1>JavaScript Operators</h1>
<h2>The -= Operator</h2>
<p>x = 10, y = 5, calculate x -= y:</p>
<p id="demo"></p>
<script>
let x = 10;
let y = 5;
x -= y;
document.getElementById("demo").innerHTML = "Value of x is: " + x;
</script>
</body>
</html>