Main page sections overlap if the browser window's width is 767px

Hello!
I’ve noticed a UI bug. It seems GitHub has no place to report UI bugs, so I report it here.

Steps to reproduce:

  1. Sign in to GitHub
  2. Go to https://github.com/
  3. Reduce the browser window’s width to 767px
  4. Scroll down until only one scroll bar is left
  5. Scroll down a bit

Actual result:


Expected result:
The sections do not overlap.

OS: Windows 10
Browser: Google Chrome 91.0.4472.164