remove grey for captions

What do I need to do to remove the grey area where captions go? I haven't been using the caption field (I just add them as regular text) because I don't like the grey background. (The tooling lines are ok, but I wouldn't mind getting rid of them too.)  You can see an example of the difference between what I want and what the theme offers toward the beginning of this post: https://explorationvacation.net/minnesota-iron-mining-history-at-hill-annex-mine-state-park/ Bonus points if I can have the text automatically italicized and centered below the image.