Custom Buttons/ Javascript Robohelp 2020

I have a dream of creating a dropdown by using a custom button and some Javascript.

But first i need help getting a custom button to talk to my javascript code.

Ive started with this simple code in the hope that if i can get this to work then i can make any button i wish.

<button onclick="myFunction()">Click me</button>

<p id="demo"></p>

<script>
function myFunction() {
document.getElementById("demo").innerHTML = "Hello World";
}
</script>

Ive tried everything can cannot get it to fire whilst using a custom button in the skins tab in robohelp2020. I could use some help.

Thanks!