reveal stack arrow icon lost on dark backgrounds.

The reveal stack arrow in binder/elsewhere is lost from view if panel background is set to generic dark-mode backgrounds / grey / dark grey / black.
A work around is required. Either:

  1. a setting enabling switching these elements to light colour when backgrounds are dark
  2. changing their default shading to a mid hue colour or colour not commonly selected as background colour, eg green or red.
  3. changing their design to a black outline arrow with white body / visa/versa - rather than solid colour so they can work in either dark or light backgrounds without the need to change their appearance.
  4. Building a proper dark-mode option in prefs for the GUI