task rows: improve DnD preview row visuals
The previews row that indicate where the row will be dropped during DnD are semi-transparent black, which is very hard to see on dark backgrounds, and totally invisible on black. They also don't actually show the real position/boundaries of the row on the horizontal axis, because they do not have an outline, and are offset horizontally on the left. This makes it hard to understand what level of hierarchy the row will end up being when dropped.
I propose simplifying the visuals and only showing the new boundaries of the row in the list, and accounting for the background color in the preview row's color (semi-transparent white for dark backgrounds, semi-transparent black for light ones). The opacity values are about 50% for the border and about 15% for the fill, but this can be fine-tuned during QA.
- define new visuals for DnD preview row
- implement new visuals
- figure out the most appropriate opacity values
- preview rows are always visible, no matter the background
- no regressions