Gutenberg gallery and Nisarg theme

I use the Nisarg theme and used the Gutenberg gallery block. It creates ugly grey boxes beneath the images for those that have captions. Does anybody know how I can get around this? I like the captions on the images.

The link is to a test site which is about as vanilla as I can make it – new install of wordpress, install Nisarg theme, upload some media and create a gallery.

The page I need help with: [log in to see the link]