This experiment hides the list of categories in the inner
sidebar for the main site settings page if the admin sidebar
is enabled. It also defaults the list of settings to "All"
instead of a specific category.
Our theory here is that people who use this page are using
it to find an exact setting, not to go through the categories
one by one. Our admin sidebar also has several groups of important
settings already too, so that can be used for browsing.
Finally, the input on the page focuses when you load it, so
filtering is faster.
Followup 203f93bcaffab1f493be70c2277ef11048f2017e
This commit makes sure the background for all the admin
site settings filters (including the filter input and
override checkbox) is consistent no matter what the theme,
as it currently changes based on theme.
This was fixed previously but must have regressed, we
are showing a darker grey background around the
"Only show overridden" checkbox for our Settings tab
in config pages.
* Fixes big gap at the left of the plugins list.
* Fixes plugin settings list padding, the yellow overridden
dot was cut off on mobile.
* Also increased settings filter input size and settings
sidebar button margin.
