[libadwaita] (3 commits) Non-fast-forward update to branch wip/exalm/backdrop

[Alexander Mikhaylenko <alexm src gnome org>]

The branch 'wip/exalm/backdrop' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  1e02b1d... stylesheet: Transparentize header bar contents for backdrop
  a23da23... stylesheet: Remove separate header bar border color for bac
  bbe3975... stylesheet: Drop public backdrop colors

Commits added to the branch:

  d6b1007... stylesheet: Transparentize header bar contents for backdrop
  cc72229... stylesheet: Remove separate header bar border color for bac
  5efd045... stylesheet: Drop public backdrop colors