Final answer:
CSS is called 'Render Blocking' because it can delay the rendering of a web page. This behavior can slow down page loading and affect user experience.
Step-by-step explanation:
CSS, or Cascading Style Sheets, is called 'Render Blocking' because it can delay the rendering of a web page. When the browser encounters a CSS file, it needs to download and parse it before it can continue rendering the rest of the page. This means that until the CSS file is loaded, the browser cannot display any content that relies on that CSS file.
This render-blocking behavior can slow down the initial rendering of a web page and result in a longer page load time. To optimize page loading speed, web developers use techniques like minimizing the use of render-blocking CSS, using media queries to load CSS files conditionally, and utilizing asynchronous loading strategies.
For example, if a web page has a large CSS file that contains styles for the entire page, and it is included in the head section of the HTML, the browser will need to download and process this CSS file before it can display any content. This delay in rendering can give users the perception of a slow-loading page. However, by using techniques like inline critical CSS or loading CSS files asynchronously, developers can improve page load times and ensure a smoother user experience.