python http server firefox css style cannot be loaded

Unlike script elements, there is no async or defer attribute to simply apply to a link element, so for years now we’ve maintained the loadCSS project to make the process of loading async CSS a little easier. There are several ways to make CSS load asynchronously, but none are as intuitive as you might expect. In this post, I aim to describe up our preferred way to do that these days, which has actually been around for years. Once split, less-critical CSS should be loaded in the background-AKA asynchronously. For sites with a small amount of overall, that alone might be enough, but if the CSS is large (say, bigger than 15 to 20kb), it can help performance to split it up by priority. Of course, at least a portion of a site’s CSS should be loaded before the page should be allowed to start rendering, and to get that initial CSS to the browser immediately, we recommend inlining (or HTTP2 server-pushing) the CSS. That’s because by default, browsers will load external CSS synchronously-halting all page rendering while the CSS is downloaded and parsed-both of which incur potential delays.

One of the most impactful things we can do to improve page performance and resilience is to load CSS in a way that does not delay page rendering.

Python http server firefox css style cannot be loaded