Dark Design improvements

[phil-flip]

There are some things about the dark design that don't quite look good. To be fair, some things have been improved in a past update, tho there still are for example the very white lines between entries and around buttons or icon color, that is still black and barely-ish visible.
I encourage the devs that work on this to install the "Dark Reader"-Extension and see themselves what CSS it fixes up. I would have submitted a PR, but I don't know how to frontend. ^^'