[libadwaita] (12 commits) Non-fast-forward update to branch wip/exalm/headerbars

[Alexander Mikhaylenko <alexm src gnome org>]

The branch 'wip/exalm/headerbars' 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:

  f67aa42... stylesheet: Move the devel headerbar style to a nested widg
  c26231e... stylesheet: Restore a backdrop state for header bar
  fbcbd82... stylesheet: Tone down the devel style
  947acce... stylesheet: Add back a backdrop state for AdwTabBar

Commits added to the branch:

  15a0e08... stylesheet: Don't hardcode view switcher indicator color (*)
  fceea5f... stylesheet: Redo color swatches (*)
  d650c24... stylesheet: Add _palette.scss (*)
  432844a... stylesheet: Use palette colors instead of magic values (*)
  a352459... stylesheet: Replace #fff by white (*)
  a904e7d... stylesheet: Add foreground colors to the palette (*)
  c2ba6ba... stylesheet: Define foreground and background colors (*)
  f102b74... stylesheet: Simplify public color casts (*)
  1bae0d4... stylesheet: Move the devel headerbar style to a nested widg
  47f2482... stylesheet: Restore a backdrop state for header bar
  7f67574... stylesheet: Tone down the devel style
  136ca2a... stylesheet: Add back a backdrop state for AdwTabBar

(*) This commit already existed in another branch; no separate mail sent