Support selecting theme on the footer

[wxiaoguang]

Fixes: #27576

[wxiaoguang]

[silverwind]

Maybe there is a better colorblind icon, like "eye with cross"? If not deemed ok, I would at least make the white part of the current icon transparent, it looks odd on dark theme.

[wxiaoguang]

Maybe there is a better colorblind icon, like "eye with cross"? If not deemed ok, I would at least make the white part of the current icon transparent, it looks odd on dark theme.

I have thought about "eye with cross", but it reads like "blind" or "closed eyes".

This icon is from GitHub:

And use transparent background: d567924

[silverwind]

A nice enhancement here would be to make it work without a page reload, e.g. send the theme change to backend in an fetch call.