To add to that point, if you manage to get screenshots you can do an image comparison using perceptual hashing [0]. The idea is to compute hashes of images and compare those, rather than scanning through each pixel.

Note that perceptual hashes should not obey the avalanche effect, so a minor difference in the two images should yield a small change in the hashes (desirable in this case). Then accept results that are within some small % error margin.

An example of a library that does this is jimp [1].

[0] https://en.wikipedia.org/wiki/Perceptual_hashing [1] https://github.com/oliver-moran/jimp#comparing-images

This is a really cool concept. Thanks.

This would be great, but would probably significantly hurt performance.

Especially if media queries come into play and we'd have to try different resolutions and ensure they're all the same.

> Especially if media queries come into play

Or even more simply: if your CSS is supposed to work on all pages of a website.

And @supports, and vendor prefixes, and animations, and print styles, and IE hacks...

running one instance for each combination for each targeted browser and browser version, lol. this would take forever