Created attachment 146580 [details]
demo of dark theme UI

This is a long-lasting issue regarding UI design. In linux gnome environment, many applications are designed for bright theme, for example, developer will use a big black 'A' letter as icon to denote font-size, grey color icon for alignment, etc. The color chosen for icons are generally darker to match the assumed bright/white background. 

However, for some other user using dark theme, the background color of control panel is black/dark grey, which makes dark icon button hardly distinguishable and recognize. I propose to use adaptive icons (at least two sets of icons, one for bright theme (dark icon)  & one for dark theme (light color icon) ), even better libreoffice can auto detect the theme is using and change icon set automatically.