how to find a certain CSS-class in XF?

[erich37]

I am looking for a certain CSS-class in XF ACP, but can not find it in the many CSS-files.
How to generally do this in XF?

I am looking for the CSS-code in the template named "register_form":

<p class="explain">

 

[James]

That class would be defined in form.css or style property @ctrlUnitCtrlExplain