Dark mode for hoverxref tooltips

[RDaxini]

This is a follow up to #2290
Is your feature request related to a problem? Please describe.
While the new tooltips do display in both dark and light mode, the tooltips themselves only show in light mode

Describe the solution you'd like
Enable dark mode tooltips for when the docs are being viewed in dark mode

Describe alternatives you've considered
Leaving the light mode tooltips to show when the docs are being viewed in dark mode... not a disaster, but not ideal

Additional context
Discussion in #2290