Styling Gallery Captions

Earlier this year I asked about how to make image captions appear on hover (as in the Jetpack tiled gallery styling) in this thread, and you gave me a very helpful answer which I have used ever since.

I’m now trying to apply the same styling to WordPress’ native gallery block, but using the same css code with .wp-block-gallery and/or .blocks-gallery-item doesn’t seem to be having the same effect.

Examples: a post with a single image vs. a post with block gallery.

I was wondering if you could tell me why that is?

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