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How To Optimize CSS Loading Times

Posted at — Nov 26, 2015

When developing a website, there are certain CSS practices which simplify your life. For instance, adding comments and indents makes your code easier to read and understand. This makes editing or altering your code much easier – something which can make you more productive.


However, the extra spaces and characters also contribute towards the size of the CSS file. A CSS file with lots of comments – for instance – tends to be quite large and heavy. This makes the CSS file to load slowly – something which slows down the overall loading time of a webpage.

Therefore, before deploying a CSS file, it is often advisable to optimize its loading time. This basically means reducing its overall size so that it loads faster. The process by which you do this is CSS minification.

Now, CSS minification is a process of removing unnecessary characters which aren’t essential for the proper execution of the CSS code. This can be accomplished in two ways: manually or using a CSS minifier. Let’s look at both options:

Optimizing CSS Manually

manual editing You can optimize CSS loading times by manually editing the CSS file(s). The goal is to eliminate anything which increases the CSS loading time. You can do this in the following ways:

  1. Combine All External Stylesheets Into A Single CSS File

Multiple stylesheets take longer to load. This is because the browser has to load each one of them. A single CSS file loads much faster. Therefore, a good approach to improve loading time is to combine all external stylesheets into one CSS file.

  1. Remove Comments

Comments are great for guiding you during development. However, they increase the overall size of a CSS file. A larger file takes longer to load. A good way to reduce file size is by removing all the comments.

  1. Remove Indents and Code Blocks

Indents and code blocks also increase the overall size of a CSS file. This is because they add extra bytes to the file. Therefore, to eliminate the extra bytes, indents and code blocks should be removed. For instance, a code block like this:


color: blue;

text-size: 90%;

font-family: Arial, Helvetica, serif;


Should be combined into a single line as follows:

p{color: blue; text-size: 90%; font-family: Arial, Helvetica, serif}

  1. Remove @import statements

When the @import statement is used to add CSS files to a webpage, it causes the files to load slower. This is because the browser can only process one @import statement at a time. Comparatively, files added using load much faster. Therefore to optimize CSS loading time, replace @import statements with tags.

  1. Minimize Inline styles and embedded stylesheets

Inline styles and embedded stylesheets lead to a significant increase in the size of a webpage. This is because they add extra bytes to a webpage. Also, unlike external stylesheets, inline and embedded CSS cannot benefit from caching. Therefore, to optimize loading time, minimize the use of inline styles or embedded stylesheets. If possible, eliminate them altogether.

Optimizing Using A CSS Minifier

Optimizing CSS manually has one drawback – it can be complex, boring and stressful. Just imagine you have to remove indents and code blocks from a CSS file with 300 lines of code. You can die of stress! Fortunately, you don’t have to go down this route. There are online tools which can automate the process for you.

These tools are called CSS minifiers. A CSS minifier is an application which can optimize your CSS files. You simply supply it with your CSS code, and it eliminates all the unnecessary characters and spaces. You can even supply it with multiple files, and it combines them into a single file. Different CSS minifiers have different features. The five most popular ones are the following.

  1. CSS Compressor
  2. CSS Minifier 
  3. Closure Stylesheets
  4. YUI Compressor
  5. CSS Minifier – Dan’s Tools

Once the CSS files are minified, you get output file that has the un-necessary parts removed. Then from your web pages, simply link to the minified CSS Stylesheet.

In a nutshell, the way to optimize CSS loading times is by reducing the number and sizes of your CSS files. You can do this either manually, or using a CSS minifier. Using a CSS minifier is simpler, hustle-free and smarter. However, CSS minifiers cannot eliminate your inline styles or embedded stylesheets. Those ones have to be eliminated manually.

Image credits: Geir Arne BrevikNic McPhee

Read More:

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