How Critical CSS can improve load speed and website rendering

For both the SEO ranking and user experience of your website, speed and performance have become very important factors. If the loading time is too long, you risk losing customers. Every millisecond you can save is valuable. Cascading Style Sheets, also known as CSS, are essential for shaping your web pages. Unfortunately, they can be an obstacle to fast loading times, as CSS files are render blocking. This means that the browser has to wait until the CSS file is fully loaded before the page is displayed correctly. The rendering of a web page can be delayed by CSS files, especially if these files are large.

A solution can be found in Critical CSS

You want to ensure that your web pages load quickly and perform optimally. This means preventing delays caused by CSS files, which can be achieved through Critical CSS. With Critical CSS, you can optimize the rendering of your website by loading only the essential styles needed for the first view of a page, while the rest of the CSS file is loaded later. But what exactly is Critical CSS, and how can we help with its implementation on your website? We’re happy to tell you all about that!

What exactly is Critical CSS?

Critical CSS is the part of your CSS that is needed to correctly display the top of the page. This is the portion of your website that visitors see first. Instead of having the browser load the entire CSS file before anything is displayed on the screen, Critical CSS loads only the essential styles needed for the first viewport. The full CSS file is then loaded asynchronously.

The difference between traditional CSS files and Critical CSS

Traditional CSS files are often loaded at the beginning of the HTML code. These files are render blocking, meaning that the browser has to wait until the full CSS file is downloaded and processed before displaying the content of the page. This can significantly slow down the load time, especially for larger websites with many styles. If a visitor has to wait too long for the web page to display properly, you risk losing them to a competitor who has ensured faster loading times for their website.

With Critical CSS, you place a small part of the CSS inline in the HTML header. This small piece of code contains only the styles necessary for displaying the top portion of the page. The rest of the CSS file is then loaded asynchronously, so it no longer impedes the initial rendering of the page.

Calculating the Critical CSS path

Determining which CSS is crucial for the first rendering of the page can be challenging and time-consuming. To avoid this, we have developed a unique tool. Our tool automatically calculates the Critical CSS path, which is the path of styles needed to render the first visible content on the page. By automating this process, you can save significant time and ensure that your website consistently loads quickly, no matter how much CSS you have.

The Critical CSS path can vary per page, depending on the unique elements and layout of each page. Our tool automatically analyzes each page and generates a piece of inline CSS that contains only the critical styles. This saves you the effort of manually identifying which styles are important, and it ensures that your website always performs optimally.

Benefits for your LCP and CLS

Optimizing your CSS through Critical CSS has a direct impact on two key web vitals: Largest Contentful Paint (LCP) and Cumulative Layout Shift (CLS). These two metrics are used by search engines like Google to assess the performance of your website. We’ll explain them in more detail and discuss the impact that Critical CSS has on these web vitals.

Largest Contentful Paint (LCP)

Largest Contentful Paint, or LCP, measures the time it takes to display the largest content block on your page, such as an image, video, or text. When your full CSS file is loaded at the start of the page, it can significantly delay the LCP. By using Critical CSS, the first parts of the page can be displayed faster, leading to a better LCP score.

Cumulative Layout Shift (CLS)

Cumulative Layout Shift, or CLS, measures the visual stability of your website. Layout shifts that occur after a page has loaded can lead to a poor user experience. These shifts often arise due to slow loading of styles. By using Critical CSS, the key styles are loaded from the start, minimizing layout shifts and improving your CLS score.

Implementation in various CMS systems

The implementation of Critical CSS can be technically complex, especially if your website runs on a content management system (CMS). We have developed tools that make this process simple for various popular CMS systems, including WordPress, Magento, Typo3, and Laravel. These tools seamlessly integrate with your existing infrastructure and allow for automatic generation and insertion of Critical CSS. We’d like to give you more insight into these processes.

WordPress

For WordPress, we have developed a plugin that automatically generates Critical CSS for every page on your site. You only need to activate the plugin, and the rest happens in the background.

Magento

For Magento users, we have developed a module that generates Critical CSS for every product page, category page, and other important pages on your website.

Typo3 and Laravel

For these platforms, we also have solutions that are easy to integrate. Our tools are designed to work with minimal configuration, allowing you to focus on your business rather than technical optimizations.

We’re here to help with implementing Critical CSS

Critical CSS is a powerful technique for improving your website’s load speed and offering a better user experience. By loading only the most essential styles needed for the first view of the page, you can significantly reduce the time it takes to render your website. At the same time, you can improve key performance metrics like LCP and CLS. We are here to help you implement Critical CSS, regardless of the CMS your website is built on. With our tools, you can easily generate and integrate Critical CSS, ensuring that your website loads faster and more efficiently. Curious about what we can do for you and the performance of your website? Contact us today to find out more!