[libadwaita] (13 commits) ...demo: Add a style classes demo page

[Alexander Mikhaylenko <alexm src gnome org>]

Summary of changes:

  491ab4c... stylesheet: Add a .card style class (*)
  599eed2... stylesheet: Add button.opaque style class (*)
  f5e0750... stylesheet: Consistently support colored styles between but (*)
  4304435... stylesheet: Support .pill for menu buttons (*)
  5ebabe5... stylesheet: Stop supporting .flat+suggested/destructive-act (*)
  1463d4d... stylesheet: More thorough entry.error and .warning styles (*)
  b38380d... stylesheet: Fix flat/outline buttons in toolbar popovers (*)
  8281a46... stylesheet: Remove overlay osd overrides for toolbars (*)
  6220614... stylesheet: Normalize padding for osd toolbars (*)
  5af9db4... stylesheet: Adjust margins for scalebuttons in toolbars (*)
  689b585... stylesheet: Fix a typo in button.osd:checked style (*)
  1f285d9... stylesheet: Allow .card on buttons as well (*)
  e49a407... demo: Add a style classes demo page (*)

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