D20968: [kcmkwin/kwindecoration] Refine drag-and-drop button removal UI

ngraham created this revision.
ngraham added reviewers: VDG, KWin.
Herald added a project: KWin.
Herald added a subscriber: kwin.
ngraham requested review of this revision.

REVISION SUMMARY
  - Reduce background opacity while dropping button to diminish visual noise
  - Increase label size
  - Re-word label for greater clarity
  - Remove redundant icon (the text is enough)
  
  BUG: 407109
  FIXED-IN: 5.16.0

TEST PLAN
  F6804039: dnd.jpeg <https://phabricator.kde.org/F6804039>

REPOSITORY
  R108 KWin

BRANCH
  refine-windeco-button-dnd-ui (branched from master)

REVISION DETAIL
  https://phabricator.kde.org/D20968

AFFECTED FILES
  kcmkwin/kwindecoration/package/contents/ui/Buttons.qml

To: ngraham, #vdg, #kwin
Cc: kwin, jraleigh, GB_2, mkulinski, ragreen, jackyalcine, Pitel, iodelay, bwowk, ZrenBot, ngraham, alexeymin, lesliezhai, ali-mohamed, hardening, jensreuterberg, abetts, sebas, apol, mart