ClaudiusH I noticed the same thing as I'm adapting one of my extensions to 2.0. I thought it was something that I needed to fix (noted it on my TODOs) but now I'm wondering if it's a Flarum 2.0 issue to fix.
Now I did a quick check and it seems to me it's because they changed the form styling and replaced .Form-group's margin-bottom: 24px; by gap: 10px (among other changes).
@IanM So now my question to the Flarum dev is: will this be addressed/fixed (so I'll leave it be for now until that fix) or should we make are own adjustments for all our extensions every time?