Describe the bug

There's a big white chunk of nothing at the bottom of the Site Editor with the Inserter open

To reproduce
Steps to reproduce the behavior:

1. Go to the experimental Site Editor
2. Click on the Inserter sidebar
3. Scroll down to the bottom of the Editor area
4. Notice that there's a huge white area of nothingness, a void if you will

Expected behavior
No void.

Editor version (please complete the following information):

• WordPress version: 5.5.1
• Gutenberg plugin version: 9.2.1

Desktop (please complete the following information):

• OS: macOS 10.15.7
• Browser: Chrome 86.0.4240.111