Regression caused by scss linting fixes

[GuySartorelli]

This PR which fixes scss linting warnings has caused a regression in symbiote/silverstripe-gridfieldextensions.

When using the GridFieldNestedExtensions component, there should be a dropdown arrow next to gridfield items:

instead, the dropdown arrow is missing:

I ran a git bisect and found the above-linked PR is what caused this bug.

You can reproduce this by using the steps in the description of this PR to set up a nested gridfield.

PRs

• FIX Restore correct margin for gridfield #1790
• FIX Restore correct margin for elemental history silverstripe-elemental#1213