You should, I think, at that point be seeing a square image of a jellyfish inside a red square. The square should be containing the image. When you hover, it should reveal the rest of the jellyfish (the image itself is rectangular, and wider than it is tall).

(I'm also using FF, and it works for me.)

yeah, I see the square jellyfish image inside the red square, but nothing changes when I hover.

I'm using Safari on Mac and it also does not work for me.

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