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 using Firefox dev, it overflows for me. Are you sure you didn't hover the earlier screenshot of the unhovered image inside the red square, as opposed to the image inside a codepen embed?
Definitely using codepen. I can manipulate the scaling and view the html and css windows and stuff. I'm not using the latest firefox version, but it's not like this is a new feature right?
Okay, I've figured it out, thanks to the "test distros online" thingy to test version 145 and 148 as I previously mentioned.[0]
From Firefox 148 release notes for developers:[1]
> The overflow, overflow-x, and overflow-y CSS properties can now be used on replaced elements such as images, in the same way that they are used with other elements. Prior to this, replaced elements were always clipped to their bounding container. (Firefox bug 1999100).
Is something supposed to happen when I hover my mouse over the image? Because nothing happens. I'm using Firefox.