Provide a color scheme for dark mode

[ThunderbirdMailDE]

It would be nice to have a color scheme for dark mode. The main issue is the light background color in this button:

A simple solution could be the use of rgba colors for the elemnts background and set alpha for this element to 50 % in dark mode.

[ThunderbirdMailDE]

rgba with alpha set to 0.5:

If the alpha 0.5 would be also in light mode:

But it's your decission, which colors you would use here.

[ThunderbirdMailDE]

A possible, working color scheme working for both dark and light mode could be:

[lieser]

I'm certainly not against changing the defaults colors to something that work good in both the light and dark mode.

Thanks for also providing possible new defaults. First impression is good but I will still take a closer look at it before changing them in the next release.

If someone else wants to try them out the new proposed defaults for easy copy paste:

• valid: rgba(0,255,0,0.5) - old value: #00FF00
• valid with warning: rgba(255,150,0,0.5) - old value: orange
• invalid: rgba(255,0,0,0.5) - old value: red

[ThunderbirdMailDE]

The transparency 0.5 could be a problem when hovering the button.