nice theme @manuel, i love your work. i may use this (or a variation of it 
) on my current forum because it looks like it would be one a lot of my user demographic would like.
question: is the nav-bar supposed to be gone on all pages? as an admin i get a blank space with one button (admin wrench) on the main categories page and so the space is quite noticeable there - but really who cares because i’m the admin and it looks great for regular users. however, i know quite a number of my users use the nav-bar filter links so a mild suggestion would be to add a setting to unhide it on the categories page.
i like how you moved the new topic button to the header and i love the favorites star.
i know you said work in progress on the rounding and i suspect you are on this, but i would suggest some description for the various settings in that component (like in the avatar TC).
i must be in the minority of those that use the collapsing navigation sidebar menu on desktop because i always miss the hamburger icon and that feature in full-width themes and i seems to be a thing these days - it was my only complaint about the Meta full width theme too (but i notice it’s back now) 