In my PG Wordpress theme I have a sidebar.
(p.s. I am testing on the Starter Theme2 pages)
In the sidebar I drag for example Pages, Recent Posts… This I do in Wordpress Appearence->Widgets.
With the CSS inspector in the browser I can find the CSS that I need to change.
For example I want to have the title from the Pages widget with a nice background color
I can find it out, but maybe I save time and someone has already clear guidelines to help me out