How to programmatically change widget properties?

I’d like to change the background color of Heading widget when someone clicks on heading text on my heading1.
I put heading1 Heading Widget on page my and I put HTML Widget with following code in it:

<script>
var response
document.getElementById("heading1").addEventListener("click", function(){
    
---AND HERE I WOLD LIKE TO CHANGE BACKROUND COLOR TRUGHT CODE---

});
</script>

Thank you!