<!DOCTYPE html>
<html>
<body>
<iframe id="myframe" src="demo_iframe.htm">
<p>Your browser does not support iframes.</p>
</iframe>
<p>Click the button to change the background color of the document in the iframe.</p>
<p id="demo"></p>
<button onclick="myFunction()">Try it</button>
<script>
function myFunction() {
var x = document.getElementById("myframe");
x.style.backgroundColor = "red";
}
</script>
</body>
</html>