The difference is that CSS can trigger remote resource loads in response to post-pageload user behavior, which intuitively seems like a JS-only thing. For examp

The difference is that CSS can trigger remote resource loads in response to post-pageload user behavior, which intuitively seems like a JS-only thing. For example, tracking where the mouse has moved, as mentioned in the readme. I wouldn't say it's some sudden, alarming capability, but it is distinctly more capable than <img> tags.