But could it be done with CSS/whatever? 
EDIT: Ignore all of the below. The issue was the Discourse Topic List Author component.
Also, any idea what happened to this bar? I refreshed my page last night and it randomly turned into this and I can’t figure out how to fix it. It still looks fine on mobile, though. The bar is really wide now and when you click on it, the text color is the same color (in light and dark modes) and things aren’t fully in the box now.
I’ve compared my theme’s CSS with yours here for the
topic-list-header and they’re the same, so I have no idea what’s causing this.