[Feature Request] Theme variable transparency support

[ms3056]

I would like to color the background in card mode to rgba(var(--ctp-accent), 0.3); but for some reason this doesn't work. I admit to now knowing why - I just know that the rgba tag works with some colors but not this one for whatever reason.

Do the current variables support this or is there something special about how this variable is being used that it would take effort to support it?

Thanks!