The quickest way to expedite this is to share your site. You can PM me if you prefer.
You need to get used to using the Browser Inspector and modifying Themes, even at a basic level. Beginner's guide to using Discourse Themes Then Developer’s guide to Discourse Themes
Use the Browser Inspector to find the right bits. Experiment. Here’s the guide for Firefox: Page Inspector - Firefox Developer Tools | MDN
It might seem a lot to learn, but it’s worth it, quite rewarding and help you administer your site more effectively in the future.