@star two (personal) nits, whether you want to implement that is completely up to your preference:
- imo there should be either always a gap between the sidebars and the center UI "cards", or no rounded corners when they touch. (stock Iceshrimp.NET issue, but noticed due to the larger sizing)
- the post action buttons' outline looks a bit too pronounced (bright / high contrast) for my taste
Edit:
technical nit, the media queries that switch the UI between desktop and mobile layouts are a bit off due to the font/UI sizing change
