Comment displaying issue

Hey guys. I've got problem with comment formatting. In one of my files the background colour and bounding box lines disappeared (not sure when that happened) from all comments and they're like shapeless beings. I cannot change it back. For example if go into "comment formatting..." and set any background colour it will be visible during comment editing but not when I finish editing and hover over the commented cell. Any ideas how to set it back to default look?

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