Inline Critical CSS

The CSS critical (or “above the fold”) collects all the CSS used to render the visible portion of the page. It is embedded before your principal CSS call and between <style></style> in a single line (minified if possible).

Inlining critical CSS help to speed up the rendering of the web pages reducing the number of requests to the server.

Generate the CSS critical with online tools or using a plugin like the one that Addy Osmani developed.