How to compress your CSS and improve performance

Optimizing your website’s loading speed relies heavily on the effective management of CSS files. With strategic compression and adherence to best practices, you can greatly enhance performance—resulting in quicker load times and an improved user experience.

What is CSS?

Cascading Style Sheets—commonly known as CSS—are a stylesheet language used to separate web content from its presentation (such as colors, layout, or fonts). While HTML and XML documents define the structure and meaning of web content, visual design is handled separately in CSS files. When stylesheets are used, the web server must send them to the browser in addition to the HTML document and any embedded media (images, videos, etc.). This can affect page load times.

The larger and more complex the CSS files are, the longer users may have to wait for the page to fully load. By compressing your CSS code, you can significantly reduce file size and improve your website’s performance. Another option for speeding up load times is lazy loading, which loads CSS files only when needed. This reduces initial loading time, since not all stylesheets are delivered upfront—only when they’re actually required.

The possibilities of CSS optimization

The loading time of a website is becoming increasingly important—especially with the rise of mobile devices and limited data connections. At the same time, the role of CSS has expanded and the stylesheet language is now increasingly taking on functions that were once handled by JavaScript. Many templates from content management systems like WordPress come with bloated CSS files, which can unnecessarily slow down the page load process. In this article, we’ll share a few tips and tricks to help you compress your CSS and improve your website’s loading speed.

1. Avoid the excessive use of inline-CSS (styles directly housed on the HTML element) if it’s not at the beginning of the HTML page. The same goes for style tags (individual CSS properties that deviate from the standard of the respective style sheets).

2. Combine multiple CSS files into a single PHP script. This way, the client only needs to request the PHP file, instead of sending an HTTP request for each stylesheet and waiting for the response. However, HTTP/2 now allows multiple parallel requests to be managed efficiently, which means individual CSS files can be loaded faster without the need for merging them beforehand.

3. Whenever possible, use shorthand properties like:
   body { margin: 20px 10px 5px 10px; }
   instead of longer declarations such as:
   body { margin-top: 20px; margin-right: 10px; margin-bottom: 5px; margin-left: 10px; }

4. Avoid over-qualifying selectors. If certain tags only ever appear within a specific element (e.g., within a list), there’s no need to include the parent element in the selector.

5. Use hexadecimal values for colors instead of the RGB notation.

6. Only use the universal selector * as a last resort. Style rules applied via the* universal selector* affect every single element on the page, which forces the browser to apply the styles broadly, slowing down rendering.

7. Reduce the file size of your CSS by removing unnecessary spaces, blank lines, and comments. For instance, you don’t need a space after colons or semicolons. You can also omit the final semicolon in a rule set. While this might make the CSS harder to read and less structured, the browser will process it significantly faster.

Since minimizing a CSS file can make it difficult to read and edit, you should always create a backup copy while the CSS is still well-structured. This makes it easier to make changes or fix errors later on.

Free online tools for CSS compression

There are various online applications for users that want to avoid the hassle of manually optimizing their CSS. With their help, you can compress your CSS. The tools take on the painstaking task of removing spaces, tabs, comments, and line breaks. Most programs are also able to convert the color code. You can directly download the result as a CSS file or copy it by using the copy and paste feature. Here are three applications:

CSS Minifier

The online application CSS Minifier can be found on cssminifier.com. Simply copy your CSS code into the “Input CSS” field and click on “Minify” to start the process. In the “Minified Output” field, you’ll see the result, which you can copy and download directly. CSS Minifier shortens the code by removing line breaks and spaces as well as deleting the final semicolon in the list. The tool can also easily convert the RGB code to the compressed HEX variant.

CSS Compressor

The web application CSS Compressor differs from CSS Minifier in that it offers a few options for customizing code compression. First, visit csscompressor.com and paste your CSS into the “CSS Source Code Input” field. You can now set the compression level. There are four different preset options to choose from, depending on how readable you want the compressed CSS to remain. By clicking “Show advanced options”, you can also manually check the desired optimization settings, such as ‘Compress colors’ and ‘Remove unnecessary backslashes’. Click “Compress” to start the compression with CSS Compressor. In addition to the result shown in the “Compressed JavaScript” field, the tool also provides information about the input and output size of your CSS file as well as the percentage of compression achieved.

Static.app CSS Minifier

Static.app CSS Minifier is a free and easy-to-use online tool designed to compress your CSS code quickly and efficiently. By removing unnecessary characters, whitespace, and comments, it helps reduce the file size of your stylesheets, leading to faster website load times and improved performance. The interface is clean and straightforward—simply paste your CSS code into the provided field, and the tool instantly delivers a minified version that you can copy or download.

Quicker loading times thanks to optimized CSS

The more extensive your website or online store is, the more reliant you are on style sheets, which in most cases are CSS. It’s no wonder that the burden on your web server constantly grows when the amount and size of CSS files both increase. If a site is opened via the client (browser), all CSS data has to be called up and passed on. This is why it’s highly recommended to optimize your style sheets. Online (such as the examples mentioned above) enable even beginner web developers to get rid of unimportant information from the CSS files. Maximizing optimization can’t be done with an application; carrying out the task yourself or hiring an expert are the only truly full-proof options.