Issue notifications "Customize" box overlaps repo header buttons #2189

Visit a repo you can edit

Click on Customize:

<img width="235" alt="Screenshot 2019-06-28 at 17 43 37" src="https://user-images.githubusercontent.com/1402241/60333696-46b29e80-99cc-11e9-9728-e01573cb9bbc.png">

See bug:

<img width="1047" alt="Screenshot 2019-06-28 at 17 42 45" src="https://user-images.githubusercontent.com/1402241/60333677-3d293680-99cc-11e9-9d27-51a78157f3b6.png">