Reduce groove opacity for greater contrast with scrollbar/slider/progressbar/dial
BUG: 444203
This change creates better contrast between the hovered/active scrollbar and its groove, enhancing visibility for color-blind users. The following Dolphin screenshots show the changes in the scrollbar and also the slider and progress bar at the bottom of the window:
This change also keeps the groove from glowing so brightly in the dark theme:
This also improves situations where the scrollbar groove is incorrectly drawn when the cursor is not over the scrollbar region, as happens with LibreOffice:
Original bug report here.