This is a little reminder that there is a CSS property for helping control what happens to images as they scale up: image-rendering.
We're quite used to the idea that scaling an image larger than its natural size (upscaling) causes it to be blurry. As awful as that is, it's the browser doing the best it can to algorithmically smooth out an image over more pixels than it has data. But let's say you'd really rather not it do that. Say the image is already pixel-y (pixel art), or you prefer the look of a pixelated upscaling.
It's a bit awkward in that the spec offers three values: auto, pixelated, and crisp-edges. Both pixelated and crisp-edges, for pixel art, appear to do the same thing to me, although the spec talks about them slightly differently (pixelated recommends the "nearest neighbor" or similar algorithm while crisp-edges isn't as specific).
Adding to the awkwardness, Chrome only supports pixelated and Firefox only supports crisp-edges, and for the deepest browser support, you gotta prefix it to -moz-crisp-edges. Fortunately, you can smash them all together and it seems fine.