Layout bug when commenting in full-screen mode

I found this bug when using Gitlab at work (12.8.7-ee), but was able to reproduce this on the public version of Gitlab as well.

The input field to write comments in full-screen mode is hidden behind the nav bar.

Screenshot_2020-03-30_at_14.28.39

To reproduce, try starting a discussion on merge request and go to the full screen mode.