Tryit Editor v2.7

Edit This Code:
<!DOCTYPE html>
<html>
<head>
<style>
#myDIV {
    border: 1px solid black;
    margin: 5px;
}
</style>

<script>
var _hmt = _hmt || [];
(function() {
var hm = document.createElement("script");
hm.src = "//hm.baidu.com/hm.js?73c27e26f610eb3c9f3feb0c75b03925";
var s = document.getElementsByTagName("script")[0];
s.parentNode.insertBefore(hm, s);
})();
</script>
</head>
<body>

<div id="myDIV">
  <p>This is a p element in div.</p>
  <p>This is also a p element in div.</p>
</div>

<p>Click the button to add a background color to the first p element (index 0) in div.</p>

<button onclick="myFunction()">Try it</button>

<p><strong>Note:</strong> The querySelectorAll() method is not supported in Internet Explorer 8 and earlier versions.</p>

<script>
function myFunction() {
    var x = document.getElementById("myDIV").querySelectorAll("p");
    x[0].style.backgroundColor = "red";
}
</script>

</body>
</html>