groups 2: chat channel header bar cuts off top of reaction modal

[tinnus-napbus]

Describe the bug
If you open the reaction modal too close to the top of the screen, the top of it is cut off by the channel header bar

To Reproduce
Steps to reproduce the behavior:

1. Go to message near top of screen
2. open reaction modal
3. observe top cut off by header bar

Expected behavior
should be shunted down below the header bar so it doesn't get cut off

Operating context

• Device: x86_64 desktop
• OS: arch linux
• Browser qutebrowser and chromium
• Landscape Version 0v1.n79p5.ksg1q.ed4bs.02de6.h2gv7.iroib.042ko.7b2cm.02s9n.o27h5