New admin styling: Checkbox alignment in Menus page for menu location is off when multiple possible locations are present

[Hanni]

When creating a menu on nav-menus.php in trunk, and the theme has multiple possible locations (such as is the case with Twenty Fourteen), the alignment of the second location checkbox falls below the section title (in this case "theme locations"), and is out of line with the previous checkbox thus not only looking untidy but introducing a level of confusion (see attached screenshot).

I had a look around and it seems that in [24566] @markjaquith pushed the checkboxes onto their own line below the section title to accommodate longer strings in non-English languages. Apparently the new admin CSS doesn't have the same issue (I played around with longer strings and couldn't reproduce the overlap issue, but I could be wrong) and so the checkboxes are no longer on their own line as was the case in 3.6, and 3.7. This is wonderful, but does therefore introduce this quirk (I think).

[Hanni]

Checkbox misalignment in trunk

[Hanni]

Problem not present in 3.7

[mattheu]

Taken a slightly different approach to the implementation, but it seems a bit more robust.

Also improved the appearance on smaller screens.

[iammattthomas]

In 26438:

Fix the alignment of checkboxes in menu location settings, and add responsive adjustments for those checkboxes. Fixes #26259, props mattheu.