One nice trick to understand about Feather Wiki's content editor is that it's just spitting out plain old HTML. Using that knowledge and a low-to-intermediate level of HTML skill, you can use the Show HTML button to enter any HTML into your Feather Wiki pages! Combine this knowledge with the ability to set custom CSS, and you'll be able to do a fair bit of customization to your pages! You can look around this wiki to see all the different ways I've leveraged the HTML to get more interesting results.
Be aware that any custom HTML entered there will not be minified when you save your wiki, so the extra whitespace may make your wiki a little bit larger if you're not careful. Also be careful to ensure that your HTML is valid—any tags that are not matched or that have a dangling end tag may cause rendering issues in your wiki!