What is critical CSS and why does it matter

Critical CSS is the part of your website's CSS that is needed to render the content visible in the viewport as quickly as possible. By inlining this CSS directly into the HTML of the page, you eliminate the need for the browser to make additional HTTP requests before rendering the above-the-fold content. This technique is particularly important for improving the loading time and overall performance of web pages, especially on mobile devices.

By prioritizing critical CSS, websites can achieve faster perceived load times, better user experience, and improved search engine optimization (SEO) rankings. The importance of critical CSS lies in its ability to enhance the speed and responsiveness of a web page, which is a significant factor for user engagement and retention.