Adwaita: Fix and simplify infobar styling

- Apply sizing regardless of style class.
- Fix bottom border not reaching the bottom corners.
- Remove unnecessary style overrides that should have been removed
  during the redesign.
9 jobs for fix-infobar-styling in 81 minutes and 12 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  .Pre
passed #677799
style-check-diff

00:02:54

 
  Build
passed #677800
fedora-x86_64

00:15:48

passed #677802
win32
msys2-mingw32

00:24:02

passed #677801
release-build

00:10:03

 
  Analysis
passed #677803
static-scan

00:47:02

 
  Docs
passed #677804
reference

00:07:11

 
  Flatpak
manual #677805
flatpak allowed to fail manual
flatpak-manual:demo
manual #677807
flatpak allowed to fail manual
flatpak-manual:icon-browser
manual #677806
flatpak allowed to fail manual
flatpak-manual:widget-factory