Controls missing in full-screen on Linux Mint and MX Linux?

[Rallydarkstrike]

Hi all - the title says it all. The control bar with the time slider/pause/etc is invisible for me on Linux Mint and MX Linux. I've tried resetting preferences, but I don't know what else to try.

The controls ARE there, but it's like they're invisible?

For example, in the attached screenshot, I am highlighting the invisible time slider with my cursor, so you see the pop-up showing what time on the slider bar that is....but the time slider and the entire control box is invisible...

Thanks for any help!