Bug report - layout bug when editing Sensei course lessons

Description

When editing a lesson in Sensei, there seems to be something causing the layout to break. I'm not sure if this is a Sensei issue, or a Learn WordPress issue.

Step-by-step reproduction instructions

1. Edit a course
2. Edit a lesson in a course
3. View the layout for the lesson

Expected behaviour

I would expect the editor to display with the same "margins" as other content being edited

Actual behaviour

It does not have any of the spacing of other content being edited, and there appears to be a weird padding or layout element applied on the left of the menu

When I test this on a clean WordPress install with Sensei installed, this does not happen, so it looks like it's a Learn specific customisation that's caused this.

Screenshots or screen recording (optional)

https://user-images.githubusercontent.com/180629/195289104-a38a4198-6fcc-4c8b-b13a-8d3cc6aa22a7.mp4

Environment information

• Brave
• M1 MacBook Pro, with Monterey

Start by reproducing the issue in the Sensei course lesson editor and compare it with a clean WordPress install using Sensei. Trace the Learn-specific customization affecting the lesson layout; done means the editor has the same margins as other edited content and no unexpected left padding.