[FeatureRequest] Add an environment variable to disable darkmode or an extra one for logo on darkmode

[Johannes Wünsch]

I have the following problem:
Send automatically switches to dark mode, when the system uses dark mode by default. This is nice in most cases, but it can be problematic with the logo in the top left corner.
The logo I am using works fine with a bright background, but it does not work at all with a dark background.

I see two solutions for this:

• Provide an environment variable to disable automatic darkmode
• Provide a seperate environment varialbe for the logo that is only used, when dark mode is active. In this case I could just adjust the logo so it looks nice in the dark mode, too.

Of course, the most flexible would be to provide both env variables.