<!DOCTYPE html>
<html>
<head>
<style>
div {
border: 1px solid black;
margin: 5px;
}
</style>
</head>
<body>
<div class="example">
<p class="child">P element with class="child" in first div with class="example". P's index is 0, and Div's index is 0.</p>
</div>
<div class="example">
<p class="child color">First P element with class="child" and "color" in second div with class="example". P's index is 0, and Div's index is 1.</p>
<p class="child color">Second P element with class="child" and "color" in second div with class="example". P's index is 1, and Div's index is 1.</p>
</div>
<div class="example">
<p class="child color">First P element with class="child" and "color" in third div with class="example". P's index is 0, and Div's index is 2.</p>
<p class="child color">Second P element with class="child" and "color" in third div with class="example". P's index is 1, and Div's index is 2.</p>
</div>
<p>Click the button to change the background color of the first p element with classes "child" and "color" inside the second div element with class="example".</p>
<button onclick="myFunction()">Try it</button>
<p><strong>Note:</strong> The getElementsByClassName() method is not supported in Internet Explorer 8 and earlier versions.</p>
<script>
function myFunction() {
var x = document.getElementsByClassName("example")[1];
x.getElementsByClassName("child color")[0].style.backgroundColor = "red";
}
</script>
</body>
</html>