Sorry. I realized midway through this discussion I’d led you down a path that required a lot of you - perhaps more than you are prepared for at this stage in your testing “journey”.
Javascript code (like my big block of code above) can be included in your test as a lengthy string of text and then executed by WebUI.executeJavaScript().
That’s a bit clunky, to say the least, but it works. Better still, I have it on good authority that the Katalon developers are bringing JavaScript to the forefront as a first-class citizen - so this clunkiness is likely to improve one day.
This (silly) example JavaScript will change the color of the page to pink:
String js = 'document.querySelector("body").style.backgroundColor = "pink";'
WebUI.executeJavaScript(js, null)
You can try the same code in the browser console
document.querySelector("body").style.backgroundColor = "pink"