improve readability of dark mode

[CWempe]

When I was playing with my family everybode was pleased when I mentioned there was a dark mode.

But everybody switched back to light mode, because it was to hard to read.

I may try to see what colors work better and add a PR when I find some time.

I will look at https://material.io/design/color/dark-theme.html for inspiration. 😎

[CWempe]

Looks like it is not as easy to manipulate the colors as I expected. I just know a little html and css. But I cannot find where the color of the text is defined. Here? But I don't know how this works. 😄

Anyway: Here is my proposal (according to material design):

original:

proposal:

1. main backgroud: #121212
2. cell background: #fff; opacity: 16% (or similar)
3. text color: #fff; opacity: 87%;

My main issue is the contrast of the cell background to the cell text. It should be more "white on back" instead of "black on grey"