Add config option to specify parent container for overlay

[r0st1kuzh]

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Is your feature request related to a problem? Please describe.
I'm always frustrated when overlay overlays zoomed image because stacking context

Describe the solution you'd like
I would like to set overlay in the same stacking context as images. Maybe add some config option to point to parent class where overlay should be rendered?

Describe alternatives you've considered
I've tried to set different z-indexes, but nothing works, overlay is either above or below the zoomed image.