CSS selectors in Ionic v3-v4?

I’m having a lot of trouble figuring out basic theming of an Ionic app. My troubles are with selectors. For example, if I want to say, change the background color to red, remove borders, and expand the side menu to full width I have no idea how to do that. I understand that I can place classes on elements but that seems incredibly limited and doesn’t always work. Is there a better readme or tutorial than the one provided by Ionic?

Sincerely, a very confused guy that can’t do colors.