Check out example codes for "changing css using js in html". It will help you in understanding the concepts better.

Code Example 1

document.getElementById("myText").className = "anyNewClass"

Code Example 2

document.getElementById(id).style.property = new style

Code Example 3

<!DOCTYPE html>
<html>
<body>

<h1 id="id1">My Heading 1</h1>


<button type="button" 
onclick="document.getElementById('id1').style.color = 'red'">

Click Me!</button>

</body>
</html>

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