Hey sorry for not getting back to you earlier! You can actually use the built-in Feather Wiki CSS for multiple columns! It's not documented anywhere yet, so I'll work on getting it added to the https://feather.wiki website when I get a chance, but here's how it works!
In the HTML, use the class "r" for row and "c" for column. It will automatically adjust the widths of the columns unless you specify a width. There also are "w12" for half the width of the space it's inside of, "w34" for three fourths (75%) of the space, "w13" for one third (33%), and "w14" for one fourth (25%), just make sure they add up to 100% otherwise it might make the layout not look right. Here's an example of 2 half-width columns:
<div class="r">
<div class="c w12">
This is the left column
</div>
<div class="c w12">
This is the right column
</div>
</div>