Maybe you've seen it maybe you didn't but it seems Joomla did introduce the "hasPopover" class. Did see several messages on the web complaining about it (people using joomla 3) and some people are overwriting files by adding custom files.. But 1 way to solve it might be to target the hasPopover classes.
Attached you'll see an example of a color-change. did it by changing the popover classes in template
Ofcourse things can be restyled more but am leaving it for now.
// image is not of JEM 2.3.0 but from custom-version running in Joomla 4