Adwaita: Make content-view subtitles smaller
Make app sections stand out a bit more
Fully separate GTK widget style from GNOME style
Don't mix up styles from different widgets.

Fixes 35070ca378eb5b6f393c19a9501300b5d1b56c52
Set focus padding to zero for notebook tabs

This interferes with the css border and padding.
Add back a bit more padding in tabs

Now that we ignore focus padding
simplify tab hover state handling
Remove reorderable tab style until we have it
Prelight tab label text
Use underline prelight on tabs instead of background
Add more contrast in tab labels
Add a little transition to tab label changes
Add a style for reorderable notebook tabs
overlap tabs 1px to avoid double border
Make the tab close button a little less blinky

Add transitions and make it less noisy on inactive tabs.
Make unfocused tab close buttons a little more visible
adwaita: Improve popover theming

Radius was reduced a bit, and a minimal padding has been added
so square contents don't occlude the rounded corners.

On dark themes, the shadow has been made the same than OSD popovers
get in light themes, so dark popovers get a light shadow in all
situations.
Drop no-longer-used color scheme from settings

GTK+ no longer uses the gtk-color-scheme setting.
Update style for GtkAssistant