Critical CSS and CSS Delivery

When a browser loads a webpage, it needs to download and process all CSS files before it can display any content. This is known as render-blocking CSS.

This lesson explores how to deliver the essential styles needed for the initial view of your page quickly, making your website feel much faster to users.

Imagine waiting for a book to be fully bound and covered before you can read even the first page. That's similar to how external CSS files can block rendering.

• The browser must download all CSS.
• It then processes these styles.
• Only after this can it paint the page.

This delay directly impacts your website's First Contentful Paint (FCP) and Largest Contentful Paint (LCP) scores.