7 best CSS optimization tips to shorten page load time

In today's web, page loading speed is one of the most important website indicators. Even milliseconds will have a huge impact on user experience and products, and slow page loading will easily reduce the conversion rate. You can use many tools and techniques to speed up your website. In this article, we will introduce the best CSS optimization techniques that can be used to improve front-end performance.

1. Find performance bottlenecks

The most important thing in all optimizations is to start with a comprehensive diagnosis. Fortunately, there are many CSS diagnostic tools that can help you find any performance bottlenecks. First, you can use the DevTools of the web browser to check the asset loading speed. In most browsers, you can open DevTools by pressing the F12 button.

For example, in Firefox DevTools, you can use the "Network" tab to check the size and load time of all CSS files loaded on the page. You can also test the speed of CSS loading with and without caching. Since DevTools also displays external CSS, such as Google font files and CSS resources extracted from third-party CDNs, you can find many resources that you didn't know before.

7 best CSS optimization tips to shorten page load time

Pingdom Tools and Lighthouse provided by Google are two other free tools that developers often use to analyze website speed and front-end performance. For example, if you run a simple website speed test, Pingdom Tools will provide you with some useful CSS optimization tips.

7 best CSS optimization tips to shorten page load time

2. Minify and compress CSS files

Most websites rely on multiple CSS files. Although in most cases modular CSS is considered a best practice, it can take a while to load all files. However, this is exactly why CSS minification and compression tools exist. If you use them appropriately, you can greatly reduce page load time.

There are some online tools, such as CSS Minify, that allow you to reduce the size of your CSS file by copying and pasting it into a simple form. This type of tool works well with smaller projects. However, for large projects with multiple CSS files, using them can become cumbersome and time-consuming. In this case, it is best to choose an automated solution.

Today, most build tools allow you to automatically perform compression on the code base. For example, by default, Webpack returns all files as minified packages. PostCSS also has smart plug-ins such as CSS Nano, which can not only reduce the file size, but also run it through many targeted optimizations.

7 best CSS optimization tips to shorten page load time

3. Use Flexbox and CSS grid

If you still rely only on the traditional box model when writing CSS, and use margins, padding, and floating points to align items on the screen, you should consider adopting more modern layout modules, namely flexbox and CSS Grid. These new models allow you to implement complex layouts with less code.

With older techniques, you even need to make many tricks and adjustments, even for simpler things, such as centering the project vertically. However, this is not the case with flexbox and CSS Grid. Although it may take some time to pick up the new layout module, it is worth it because the CSS file is much smaller. This is especially true for flexbox. So far, flexbox has pretty good browser support (currently 98.3% globally).

7 best CSS optimization tips to shorten page load time

Although the browser's support for CSS Grid is not complete (currently accounting for 92.03% of the world), you can still use it if you don't have to support older browsers or are willing to provide backup features.

7 best CSS optimization tips to shorten page load time

4. Use the <link> tag instead of the @import rule**

You can use two main techniques to make web pages load CSS files:

Use the <link> tag to add them to the <head> section of the HTML page,

Use *@import *CSS rules to import them from other style sheets.

You need to add the @import rule to the top of the main CSS file. In most cases, it is used to load smaller resources, such as fonts and other design elements. Initially, this seemed to be a good solution, but compared to HTML pages using the <link> tag to load the style sheet directly, it takes a lot longer for the browser to load the additional style sheet.

When you add multiple CSS files to an HTML page, be sure to pay attention to the specificity of CSS. Add the most general style sheet first, and then choose a more specific style sheet. You need to do this because the style sheets added later will override the rules of the previous CSS file. For example, the following example adds CSS files in the correct order:

<link rel="stylesheet" href="main.css"><link rel="stylesheet" href="page.css"><link rel="stylesheet" href="component.css">

5. Use gradients and SVG instead of images

It can take a lot of time to load all the images on a web page. Developers use many image optimization techniques to mitigate this impact, such as loading images from an external CDN or using image compression tools such as TinyJPG. These solutions can provide a lot of help, but in many cases, you can use native CSS effects to replace a large number of resource JPG and PNG images.

For example, you can use gradients instead of background images, and background images may greatly slow down the user's browser. You can use the gradient function of CSS to create linear, radial and repeating gradients. Using these native CSS features, you can not only define the color, but also the angle of the gradient.

For example, the following rule creates a nice gradient background that loads faster than any image:

div {    background: linear-gradient(45deg, lightgreen, royalblue);

For more complex gradients and textures, you can also use generators such as CSSmatic (shown below) and ColorZilla.

7 best CSS optimization tips to shorten page load time

In addition to gradients, you can also use Scalable Vector Graphics (SVG) to replace traditional JPG and PNG images. Not only do they load faster, but you only need to include one version of the image. This is because SVG can be scaled up to any size without any quality loss due to its vector nature. In addition, you can also use CSS to style SVG, just like normal HTML files.

6. Avoid important rules

in spite of! The important rule may be a godsend in some situations, but you should only use it as a last resort. This rule creates an exception from the cascade. Therefore, when you add in the CSS declaration! When important, it will overwrite all other declarations, even those with higher specificity. Its syntax is as follows:

h1{  margin-bottom: 20px!important;

If there are too many important rules in the CSS, the user's browser will have to perform additional checks on the code, which may greatly reduce the page speed. As a rule of thumb, never use it for site-wide CSS or when creating themes or plugins! important. If possible, use it only when you want to overwrite CSS from a third-party library.

7. Consider CSS refactoring

Although CSS refactoring is rarely an easy task, in many cases it can significantly improve website performance. For example, if the CSS file is too large, or you have inherited an old code base, or the page load time is poor, severely hurting the conversion rate. The goal of CSS refactoring is to make the code cleaner, more maintainable and faster to load.

CSS refactoring is a multi-step process, during which you need to analyze all aspects of the CSS code base. You need to check a few different things, such as:

Whether you have unused or repeated CSS rules or resources,

Is it possible to use more modern technologies such as Flexbox and CSS grids,

Whether to use too much specificity (you can use this visual specificity calculator to calculate),

Whether the structure of the CSS file is reasonable (for example, it is easier to maintain a smaller file than a larger file),

Is it worth using automated build tools,

And many others

Before you start refactoring, you should also set measurable goals and choose a benchmark to use, such as page load time or the first meaningful draw so that you can compare their before and after values.

Also don't forget to use a version control tool, such as Git. This way, if there are any problems, you can go back to the previous version of the code.

wrap up

You can use many CSS optimization techniques to improve the performance of your website. Most of them are easy to implement, but can have a significant impact on page load time. Faster page loading not only enhances the user experience, but also helps you get better rankings in Google and other search engines.

In addition to CSS optimization best practices, you can also use many other techniques to improve loading speed, such as caching, Google AMP, and HTTPS protocol.

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