Do you know how to use dev tools? They come with any browser. For Chrome, the Chrome Dev Tools (right click, inspect in Chrome) can help you find the bit of html in the DOM you’d like to change. There’s a little arrow tool in the upper left corner of the tools. Click that and then you can hover over the area in question and it should show that bit of code. You can then see the class/id names and the CSS being applied. You can play with the CSS in the tools but remember that those changes are only seen by you and will change once the page is refreshed.
That should help you find the proper classes to change!