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Wednesday, September 22, 2021 at 12:33 AM

Instructions on How to Optimize CSS for Maximum Site Performance

Even in the year 2021, web performance continues to be an issue. According to HTTP Archive, the typical website needs a 2 MB download and more than 60 HTTP requests to completely load on a mobile device, and it may take up to 18 seconds to fully load on a desktop computer. Stylesheets take up 60 kB and are distributed over seven requests, thus they are seldom given high priority when trying to resolve performance problems.

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CSS, on the other hand, has an impact, no matter how little it seems. After you've dealt with your JavaScript issues, understanding how to correctly optimize CSS should be your next step.

What Role Does CSS Play in Page Performance?

CSS seems to be straightforward, yet it may require a significant amount of processing.

CSS Is a Render-Blocking Feature

As soon as your browser sees the link> tag, it temporarily suspends all other browser downloads and processing in order to retrieve and parse the CSS file.

JavaScript may also cause the browser to stall, although asynchronous processing is available using the following libraries:

The async property is used to download scripts in parallel, which are then executed as soon as they are completed.

The defer property causes downloads to occur in parallel and then execute in sequence once the DOM is complete.

Using the type="module" tag, you may load an ES module into your browser (which behaves like defer).

Assets such as pictures often use more bandwidth, although there are efficient formats available, and they may be lazy-loaded (using the loading="lazy" property) without causing the browser to pause while it renders the page.

CSS does not allow for any of these possibilities. Although the file has been cached, future page loads should be quicker; nevertheless, the render-blocking process has not been stopped.

Large CSS files take a long time to load and process.

The greater the size of your stylesheet, the longer it will take to download and convert into a CSS Object Model (CSSOM), which can then be used to display the page by the browser and JavaScript APIs. Despite the fact that CSS stylesheets are smaller than the majority of other website files, they are not exempt from the general rule that "smaller is better. "

CSS Files Continue to Grow

It may be difficult to recognize styles that are no longer in use, and deleting the incorrect styles can have disastrous consequences for a website. Developers usually opt for the most conservative method of "retaining everything. " CSS retains the existence of page styles, components, and widgets that are no longer in use on the web. As a consequence, what happened? Due to the exponential growth in the size, complexity, and maintenance burden of the files, developers are becoming less and less inclined to delete duplicate code.

Stylesheets are capable of referencing other assets.

CSS may refer to other stylesheets by referencing them using @import rules. These imports prevent the current stylesheet from being processed and instead load further CSS files in a sequence.

Additionally, other materials, such as typefaces and pictures, may be referred to. However, when in doubt, the browser will retrieve the files quickly, regardless of how efficient the download is. Base64-encoded files that are inlined are subjected to additional processing.