Inline popup editor background fix

[Ryanseanlee]

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[Ryanseanlee]

This is what is currently happening when in dark mode.

I am not sure if this is the exact fix we want but this will give the popover a background

[TomTirapani]

Thanks Ryan, this looks great! The CSS certainly looks like we're targetting the right selector and fixing the problem... however, I would recommend we use var(--xh-grid-bg); so it looks more part of the grid. var(--xh-popup-bg); default gray looks a bit like a disabled field to my eyes.