Optional background in image preview

[kam193]

Is your feature request related to a problem? Please describe.
When an image has a transparent background and colours similar to the current AL theme, it's quite difficult to see what is on it. v

Describe the solution you'd like
It would be great to have a button to turn dark/light background in the full-site image preview.

Describe alternatives you've considered

• static, always on background would just move the problem;
• it could be just one background available - in the colour contrasting to the AL theme;

Additional context

An example of the problem:

The small preview is not that bad, and it changes background on hover:

But trying to see more is hard: