CSS compression tool CSSO: A practical guide to improving website performance

This article is excerpted from Tiffany's latest book "CSS Master, Second Edition". On the road to becoming a CSS master, it is crucial to master the troubleshooting and optimization skills of CSS. How to diagnose and fix rendering issues? How to make sure CSS doesn't affect end user performance? How to ensure the quality of the code?

The appropriate tools can ensure efficient front-end operation. This article will focus on CSS compression technology.

Developer tools help find and fix rendering issues, but how efficient is it? Is our file size small enough? At this time, we need to use compression tools.

In CSS, compression is simply to "remove unnecessary characters". For example, consider the following code block:

<code>h1 {
    font: 16px / 1.5 'Helvetica Neue', arial, sans-serif;
    width: 80%;
    margin: 10px auto 0px;
}</code>

This code contains line breaks and spaces, with a total of 98 bytes. Let's look at the compressed example:

<code>h1{font:16px/1.5 'Helvetica Neue',arial,sans-serif;width:80%;margin:10px auto 0}</code>

Now our CSS is only 80 bytes – a 18% reduction. Of course, the fewer bytes, the faster the download speed and the lower the cost of data transmission, which is good for you and your users.

This article will introduce CSS Optimizer (CSSO), a Node.js-based compression tool. To install CSSO, you first need to install Node.js and npm. npm is installed as part of the Node.js installation process, so you only need to install one package.

Using CSSO requires you to be familiar with the command line interface. Linux and macOS users can use terminal applications (macOS is an application > terminal application). If you are using Windows, use the command prompt. Go to the Start or Windows menu and type cmd in the search box.

Installation CSSO

After installing Node.js and npm, you can install CSSO. On the command line, type:

<code>npm install -g csso</code>

-g flags to install CSSO globally so that we can use it in the command line. After the installation is complete, npm will print a message to your terminal window.

Now, we are ready to compress CSS.

Compress using CSSO

To compress the CSS file, run the csso command and pass the file name as a parameter:

<code>csso style.css</code>

This will perform basic compression. CSSO removes unnecessary spaces, extra semicolons, and comments in CSS input files.

After completion, CSSO will print the optimized CSS to standard output, that is, the current terminal or command prompt window. However, in most cases, we want to save the output to a file. To do this, please pass the second parameter to csso - the name of the compressed file. For example, if we want to save the compressed version of style.css as style.min.css, we will use the following command:

<code>csso style.css style.min.css</code>

By default, CSSO rearranges parts of CSS. For example, it merges declaration blocks with duplicate selectors and removes some overwritten attributes. Consider the following CSS:

<code>h1 {
    font: 16px / 1.5 'Helvetica Neue', arial, sans-serif;
    width: 80%;
    margin: 10px auto 0px;
}</code>

In this code segment, margin-left overrides the previous margin declaration. We also reused h1 as a selector for continuous declaration blocks. After optimization and compression, we get:

<code>h1{font:16px/1.5 'Helvetica Neue',arial,sans-serif;width:80%;margin:10px auto 0}</code>

CSSO removes unnecessary spaces, newlines and semicolons and shortens #ff6600 to #f60. CSSO also merges the margin and margin-left properties into a declaration (margin: 20px 30px 20px 0) and combines our separate h1 selector blocks into one.

If you are skeptical about how CSSO rewrites CSS, you can disable its refactoring feature. Just use the --restructure-off or -off logo. For example, running csso style.css style.min.css -off will get:

<code>npm install -g csso</code>

Now our CSS is compressed, but not optimized. Disabling refactoring will prevent your CSS file from reaching the minimum size. Avoid disabling refactoring unless you encounter problems.

Preprocessors and postprocessors such as Sass, Less, and PostCSS provide compression capabilities in their toolsets. However, using CSSO can further reduce file size.

To learn more about CSS debugging and optimization, please check out Tiffany's book "CSS Master, Second Edition".

Related articles:

• CSS debugging and optimization: Code Quality Tools
• CSS debugging and optimization: browser-based developer tools

Frequently Asked Questions about CSSO and CSS Compression

What is CSSO and why is it important in CSS optimization?

CSSO, or CSS Optimizer, is a tool for optimizing cascading stylesheets (CSS) files. CSS is a language used to describe the appearance and format of documents written in HTML or XML. CSSO works by minimizing the size of CSS files, which can significantly improve the loading speed of your website. This is crucial because faster loading speeds can enhance the user experience and may improve your website's ranking in search engines.

How does CSSO work?

CSSO reduces its size by analyzing your CSS code and applying various transformations. These transformations include removing unnecessary spaces and comments, merging the same selectors and attributes, and even rewriting the attribute values ??into shorter forms. The result is a smaller, more optimized CSS file that functions exactly the same as the original file.

How to use CSSO?

CSSO can be used as a command line tool or as a Node.js module. To use it as a command line tool, you need to install it globally using npm (Node package manager). After installation, you can run CSSO on any CSS file using the command "csso [input file] [output file]". To use it as a Node.js module, you need to install it locally in your project and then reference it in your script.

What are the benefits of using CSSO compared to other CSS compressors?

CSSO can not only minimize CSS files, but also optimize CSS structure. This means it can merge the same CSS selector, remove redundant properties, and even rewrite the property values ??into a shorter form. This will result in smaller file sizes compared to other CSS compressors that remove only spaces and comments.

Will CSSO break my CSS code?

While CSSO is designed to optimize your CSS without affecting its functionality, in some cases it may break your CSS. This is usually caused by errors in CSSO or improper use. After applying CSSO, be sure to thoroughly test your website to make sure everything works properly.

How to debug CSSO problems?

If you are having issues with CSSO, you can use the "--debug" option at runtime for more detailed information about how it performs. This can help you identify any problematic areas in your CSS. Also, you can restore to the original CSS file at any time if needed.

Can I use CSSO with other CSS preprocessors such as SASS or LESS?

Yes, you can use CSSO with other CSS preprocessors. However, you need to compile SASS or LESS code into regular CSS first, and then run it through CSSO.

Is CSSO compatible with all browsers?

CSSO optimizes your CSS code without changing its functionality, so the generated CSS should be compatible with all browsers that support the original CSS. However, after applying CSSO, it is best to test your website in a different browser to ensure compatibility.

Can I control the optimization level in CSSO?

Yes, CSSO provides some options that allow you to control the optimization level. For example, you can disable structural optimization or preserve comments if needed.

Is CSSO free to use?

Yes, CSSO is an open source tool, which means it is free to use. You can find its source code on GitHub and, if you prefer, participate in its development.

This response maintains the image format and placement, rewrites the text for originality while preserving the meaning, and addresses all the requirements.

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