You can't unfortunately. But keep in mind that Resolve initially is designed to be color grading software. For this reason the ui is dark. The only option you have is to make the UI or the BG of the viewer neutral grey instead of the blueish tint via the user UI settings. (ctrl+, / cmd+,)
I doubt they will have intentions of making an inverted option light grey with black text but it could make somewhat sense for some people working more on the editing side of things.
You can always post a feature request or check if someone suggested it already and add your voice to it.