Editor Layout: open sidebar menu over editor on small screens

[creativecoder]

Description

When a sidebar menu is opened on small screens, open the menu on top of the editor content, rather than squishing the content. This mainly applies to the widgets editor.

Before	After

Additionally, remove the negative margin that causes the content to jump when the menu is opened in the page/post/site editors.

Before	After

How has this been tested?

On small screens (that show the mobile version of wpadminbar)

Widget editor

1. Activate a non-block theme
2. Navigate to Appearance > Widgets
3. Test opening and closing the wp-admin navigation sidebar menu

Post/page/site editor

1. Navigate to the editor
2. Test opening and closing the wp-admin navigation sidebar menu

Types of changes

Bug fix, more or less

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR. (n/a)

[jasmussen]

Thanks for the PR! This seems to work well for me and fix the issue. Though looking at when/why those mixins were introduced in the first place, there seemed to be a good reason. See #21661 and #19011. I could'nt reproduce the original issue so it may be moot, but be sure to test with and without fullscreen mode.

[creativecoder]

Though looking at when/why those mixins were introduced in the first place, there seemed to be a good reason. See #21661 and #19011. I could'nt reproduce the original issue so it may be moot, but be sure to test with and without fullscreen mode.

Thanks for that context @jasmussen ! I double checked small and medium screen sizes and toggling full screen mode when available: I also was not able to reproduce the original issue in #19011.

[jasmussen]

Let's try it.

[david-szabo97]

LGTM 🚢 ✅

[vindl]

Works as expected!

I noticed there is a similar issue with Navigation screen (needs to be enabled in Gutenberg experiments) that would be a nice follow-up item.