Is there a tool to run CSS 1 line at a time?

I want to see how the site would load on v开发者_运维技巧ery slow connections.

Don't know about the specific answer to your question, but how about a tool that would simulate a slow connection Firefox Throttle from previous SO question

CSS isn't downloaded and "run" 1 line at a time. The whole CSS is parsed at once after downloading and the styles are applied to the whole document tree.

Is that even how CSS would be handled across a slow connection? I don't know the answer to that, but you'd probably be better of using some kind of a proxy tool to simulate slow connections.

I know Charles has this feature.

There is no line by line processing but for sure browsers implement algorithms for partially parsing and rendering blocks of CSS code even I don't think you can simulate this effect by throttling connections.