How to add CSS to HTML (Link, Embed, Import & Inline styles)

How to add CSS to HTML

(With Link, Embed, Import and Inline styles)

Adding CSS to HTML can be confusing because there are many ways to do it.

CSS can be added to HTML by linking to a separate stylesheet file, importing files from existing stylesheets, embedding CSS in a style tag, or adding inline styles directly to HTML elements. Many of these methods can also be done with javascript.

Today we're going to explore the pros and cons of each CSS method, see how they work, and learn when to use each one.

We'll cover how to:

  1. Link to a stylesheet file;
  2. Embed CSS with a style tag;
  3. Add inline styles to HTML elements;
  4. Import a stylesheet file; and how to
  5. Inject CSS with javascript.

We’ll also cover some of the common questions developers have when inserting CSS into HTML documents:

Let’s get started.

This is the most common method of attaching CSS rules to HTML documents.

With this method, all your style rules are contained in a single text file that's saved with the .css extension. This file is saved on your server and you link to it directly from each HTML file. We use a link tag which is a simple line of HTML that you put in the head section of your HTML document, it looks like this:

<link rel="stylesheet" type="text/css" href="mystyles.css" media="screen" />

The rel attribute is set to stylesheet to tell the browser that the linked file is a Casscading Style Sheet (CSS).

If you're using HTML5, the type attribute is not required, you can remove it and save a few bytes per page.

The href attribute is where you specify the path to your CSS file.

If the CSS file is in the same folder as your HTML file then no path is required, you only need to specify the filename like in the example above.

If it's saved in a folder, then you can specify the folder path relative to the HTML file like this:

<link href="foldername/mystyles.css" ... >

You can also specify a path relative to the root of your domain by prefixing with a forward slash like this:

<link href="/foldername/mystyles.css" ... >

Absolute URLs also work:

<link href="https://www.yourdomain.com/foldername/mystyles.css" ... >

The media attribute in a link tag specifies when the CSS rules are to be applied. Here are the most common values:

Advantages of linking to a separate CSS file

Disadvantages

You can include as many CSS files in your HTML document as you like by adding multiple link tags, just remember, each file requires an additional HTTP request.

2. How to embed CSS with a style tag

You can embed CSS rules directly into HTML documents by using a style tag. Here's what this looks like:

<style type="text/css" media="screen">

/* Add style rules here */

</style>

Similar to the link tag, the type attribute can be omitted for HTML5, and the media value controls when your styles are applied (leave it off to default to all devices).

Add your CSS rules between the opening and closing style tags and write your CSS exactly the same way as you do in stand-alone stylesheet files.

CSS rules are render-blocking so it's recommended to add style tags into the of HTML documents so they download as soon as possible. We'll discuss render-blocking CSS shortly.

Advantages of embedded style tags

Disadvantages

3. How to add inline styles to HTML elements with the style attribute

Style rules can be added directly to any HTML element. To do this, simply add a style attribute to the element then enter your rules as a single line of text (string of characters) for the value.

Here's an example of a heading with inline styles:

<h2 style="color:red; background:black;">This is a red heading with a black background</h2>

Advantages of inline styles

Disadvantages

4. How to load a stylesheet file with the @import rule

Another interesting way to add CSS to an HTML page is with the @import rule. This rule lets us attach a new CSS file from within CSS itself. Here's how this looks:

@import "newstyles.css";

Just change "newstyles" to the name of your CSS file and be sure to include the correct path to the file too. Remember the path is relative to the current CSS file that we are in, if the CSS is embedded into the HTML page then the path is relative to the HTML file.

Advantages of the @import rule

Disadvantages

5. How to inject CSS with javascript

Sometimes we need to apply CSS from within Javascript. We can do this in the following ways:

Inject an external stylesheet file with javascript

To do this we create a link element, add our CSS file path as the href attribute value, then inject it into the page with javascript:

/* create the link element */
var linkElement = document.createElement('link');

/* add attributes */
linkElement.setAttribute('rel', 'stylesheet');
linkElement.setAttribute('href', 'mystyles.css');

/* attach to the document head */
document.getElementsByTagName('head')[0].appendChild(linkElement);

Insert a block of rules into a page with javascript

This method creates a style element, inserts our CSS rules as a string, then attaches the element to the HTML head.

/* specify our style rules in a string */
var cssRules = 'h1 { color:black; background:red; }';

/* create the style element */
var styleElement = document.createElement('style');

/* add style rules to the style element */
styleElement.appendChild(document.createTextNode(cssRules));

/* attach the style element to the document head */
document.getElementsByTagName('head')[0].appendChild(styleElement);

Add inline styles to individual elements with javascript

In this method we first get a handle on the element(s) we want to change, then we add CSS properties.

/* get a handle on the element */
var element = document.querySelector('h2');

/* add css properties */
element.css.color = 'blue';
element.css.backgroundColor = 'yellow';

Important note: Multi-word CSS properties have their hyphen's replaced with camel case, so background-color becomes backgroundColor.

CSS and page performance

So now we’ve covered all the methods of adding CSS to HTML the next step is to learn how to put them all together and improve your website speed.

How to minify CSS to speed up your website

CSS in its hand-written state is quite verbose. We can reduce its file size by a process of minification.

What is CSS minifying?

Minifying CSS is the process of removing redundant data without affecting the browser's rendered output, this includes removing whitespace, line breaks, comments, unused code, and switching to shorthand properties to save space.

I recommend using CSS minifyer, it's a free online tool. Just make sure you keep a copy of your unminified CSS as your source code.

How to inline your above-the-fold CSS to improve page render time

If you want your page to load really fast then you need to prioritise your above-the-fold content.

Above-the-fold content is any content that is visible in the viewport before you scroll down the page, naturally, this will be different for different sized devices and screens.

There is no exact answer to where the 'fold' is - you need to decide how far down the page is right for you based on the screen sizes of your website visitors. Check your site statistics for insights on this.

Once you've made a call on your page fold, identify all elements that appear above it, then inline their CSS in a style tag.

Next, link to your main stylesheet in a non-render-blocking way. For most modern browsers you can do this by adding the following attributes to your link tag:

<link href="mystyles.css" rel="preload" as="style">

Check async CSS loading on icanuse.com for the latest support stats.

If you need to support older browsers, use the loadCSS polyfill which does the same thing with javascript.

This method works by utilising browser caching for the main stylesheet and maximises rendering speed by inlining CSS that's required for the initial page load, very neat!

Use minimal CSS for additional speed gains

The most important thing you can do to stop CSS slowing down your website is to use as little as possible. It's surprising how little CSS you need to make a beautiful-looking website.

I personally aim for a stylesheet small enough to be inlined on every page eliminating extra HTTP requests. This ensures my pages load with a single request (not including images).

Conclusion

So now you've learned all the methods of adding CSS to HTML and you've seen how they can work together to speed up your website.

I hope you've found this tutorial valuable.

Next up:
Experimental web design ideas »

Updated: 3 Sep 2018

First published: 18 Feb 2009