Floating horizontal scroll on diffs

Issue Summary

When you are trying to see a diff on a Pull Request and the PR contains a file that is wider and longer than the screen, to scroll to the right, the user needs to scroll to the bottom of the file, where the horizontal scroll bar can be found. It makes really hard to get back to the wider line and work.

Steps to Reproduce

1. Create a PR that contains a file that is wider and longer than the screen.
2. For example, we’d like to read line #7, which happens to be 6653 characters long.
3. To scroll to the right, the user needs to scroll to the bottom of the file, where the horizontal scroll bar can be found (366 lines down from line 7).
4. The user scrolls to the right by some amount.
5. The user scrolls back up to line 7 to read more of the text.
6. Repeat the process as many times as it takes to read what you need.

Workaround

Currently, there is no known workaround for this behavior. A workaround will be added here when available