Customizer menu details sizing

[Clorith]

The current styling for the menu item wrapper sets a max width of 382px, which is great, until you get a larger monitor, and the percentage widths elsewhere start making the customizer sidebar larger.

[Clorith]

Screenshot before applying max-width

[Clorith]

Screenshot after applying max-width

Trac ticket: https://core.trac.wordpress.org/attachment/ticket/51647/

[garrett-eclipse]

Thanks for the catch and fix there @Clorith, I'm envious of the massive monitor had to zoom down to 67% to reproduce. The PR fixes the issue as expected and applies cleanly.

As it's small, isolated and related to the recently committed [49346]/#49375 I'm going to see if we can land before Beta3 in 5.6.

[Clorith]

For anyone else who may be looking to test visual things in the customizer, you can also extend the width of the sidebar to get the same effect as zooming in here, but maintain your aspect ratios :)

[desrosj]

In 49481:

Customize: Ensure menu items expand horizontally on large screens.

Props clorith, garrett-eclipse.
Fixes #51647.

Merged in https://core.trac.wordpress.org/changeset/49481.