Preview theme logo and favicon

Here is a suggestion to handle this, c&c are welcome. Thanks!

For composer patching.

Hi,

After applying the fix proposed in https://git.drupalcode.org/project/drupal/-/merge_requests/4576#note_198895, here is the result with ui_suite_bootstrap.

And here is the result with Olivero.

So I wonder if something needs to be done to handle background color?

Fixed version

I agree with #5 ✨ Preview theme logo and favicon Needs work , something should probably be done in case we have a logo with a lot of white and transparency, as we with the one included in Olivero.

Maybe have two preview boxes for each image (with a light border), one with a white background, one with a black / dark grey background?

I agree with the background issue. I'm just not sure how to adress it. Should we leave a css is on the wrapper div and place the styles somewhere in the core itself (where?) or directly put a style attribute (which seems a bit dirty no?).

I think the only goal for core system module is to display logo + favicon. The rest for for themes (background, colours, etc).
But not sure if it should be separate issue for theming

For uploaded logotypes / favicons would be (maybe) nice to have `cross` icon above the image to be able to quickly remove it. Pretty obvious behavior to me