How can I define colors as variables in CSS?

I’m working on a CSS file that is quite long. I know that the client could ask for changes to the color scheme, and was wondering: is it possible to assign colors to variables, so that I can just change a variable to have the new color applied to all elements that use it?

Please note that I can’t use PHP to dynamically change the CSS file.

CSS supports this natively with CSS Variables.

Example CSS file

:root {
    --main-color:#06c;
}

#foo {
    color: var(--main-color);
}

For a working example, please see this JSFiddle (the example shows one of the CSS selectors in the fiddle has the color hard coded to blue, the other CSS selector uses CSS variables, both original and current syntax, to set the color to blue).

Manipulating a CSS variable in JavaScript/client side

document.body.style.setProperty('--main-color',"#6c0")

Support is in all the modern browsers

Firefox 31+, Chrome 49+, Safari 9.1+, Microsoft Edge 15+ and Opera 36+ ship with native support for CSS variables.

People keep upvoting my answer, but it's a terrible solution compared to the joy of sass or less, particularly given the number of easy to use gui's for both these days. If you have any sense ignore everything I suggest below.

You could put a comment in the css before each colour in order to serve as a sort of variable, which you can change the value of using find/replace, so...

At the top of the css file

/********************* Colour reference chart****************
*************************** comment ********* colour ******** 

box background colour       bbg              #567890
box border colour           bb               #abcdef
box text colour             bt               #123456

*/

Later in the CSS file

.contentBox {background: /*bbg*/#567890; border: 2px solid /*bb*/#abcdef; color:/*bt*/#123456}

Then to, for example, change the colour scheme for the box text you do a find/replace on

/*bt*/#123456

CSS itself doesn't use variables. However, you can use another language like SASS to define your styling using variables, and automatically produce CSS files, which you can then put up on the web. Note that you would have to re-run the generator every time you made a change to your CSS, but that isn't so hard.

Yeeeaaahhh.... you can now use var() function in CSS.....

The good news is you can change it using JavaScript access, which will change globally as well...

But how to declare them...

It's quite simple:

For example, you wanna assign a #ff0000 to a var(), just simply assign it in :root, also pay attention to --:

:root {
    --red: #ff0000; 
}

html, body {
    background-color: var(--red); 
}

The good things are the browser support is not bad, also don't need to be compiled to be used in the browser like LESS or SASS...

Also, here is a simple JavaScript script, which changes the red value to blue:

const rootEl = document.querySelector(':root');
root.style.setProperty('--red', 'blue');

You can try CSS3 variables:

body {
  --fontColor: red;
  color: var(--fontColor);
}

There's no easy CSS only solution. You could do this:

• Find all instances of background-color and color in your CSS file and create a class name for each unique color.

    .top-header { color: #fff; }
    .content-text { color: #f00; }
    .bg-leftnav { background-color: #fff; }
    .bg-column { background-color: #f00; }
  

• Next go through every single page on your site where color was involved and add the appropriate classes for both color and background color.

• Last, remove any references of colors in your CSS other than your newly created color classes.

The 'Less' Ruby Gem for CSS looks awesome.

http://lesscss.org/

Yes, in near future (i write this in june 2012) you can define native css variables, without using less/sass etc ! The Webkit engine just implemented first css variable rules, so cutting edge versions of Chrome and Safari are already to work with them. See the Official Webkit (Chrome/Safari) development log with a onsite css browser demo.

Hopefully we can expect widespread browser support of native css variables in the next few months.

Do not use css3 variables due to support.

I would do the following if you want a pure css solution.

1. Use color classes with semenatic names.

    .bg-primary   { background: #880000; }
   
    .bg-secondary { background: #008800; }
   
    .bg-accent    { background: #F5F5F5; }
   

2. Separate the structure from the skin (OOCSS)

    /* Instead of */
   
    h1 { 
        font-size: 2rem;
        line-height: 1.5rem;
        color: #8000;
    }
   
    /* use this */
   
    h1 { 
        font-size: 2rem;
        line-height: 1.5rem;
    }
   
    .bg-primary {
        background: #880000;
    }
   
    /* This will allow you to reuse colors in your design */
   

3. Put these inside a separate css file to change as needed.

Sure can, sort of, thanks to the wonderful world of multiple classes, can do this:

.red {color:red}
.blackBack {background-color: black}

but I often end up combining them anyway like this:

.highlight {color:red, background-color: black}

I know the semantic police will be all over you, but it works.

I'm not clear on why you can't use PHP. You could then simply add and use variables as you wish, save the file as a PHP file and link to that .php file as the style sheet instead of the .css file.

It doesn't have to be PHP, but you get what I mean.

When we want programming stuff, why not use a programming language until CSS (maybe) supports things like variables?

Also, check out Nicole Sullivan's Object-oriented CSS.

You can group selectors:

#selector1, #selector2, #selector3 { color: black; }

You could pass the CSS through javascript and replace all instances of COLOUR1 with a certain color (basically regex it) and provide a backup stylesheet incase the end user has JS turned off

dicejs.com (formally cssobjs) is a client-side version of SASS. You can set variables in your CSS (stored in json formatted CSS) and re-use your color variables.

//create the CSS JSON object with variables and styles
var myCSSObjs = {
  cssVariables : {
    primaryColor:'#FF0000',
    padSmall:'5px',
    padLarge:'$expr($padSmall * 2)'
  }
  'body' : {padding:'$padLarge'},
  'h1' : {margin:'0', padding:'0 0 $padSmall 0'},
  '.pretty' : {padding:'$padSmall', margin:'$padSmall', color:'$primaryColor'}
};

//give your css objects a name and inject them
$.cssObjs('myStyles',myCSSObjs).injectStyles();

And here is a link to a complete downloadable demo which is a little more helpful then their documentation : dicejs demo

EDIT: This answer is no longer current. You should use CSS variables now.

Consider using SCSS. It's full compatible with CSS syntax, so a valid CSS file is also a valid SCSS file. This makes migration easy, just change the suffix. It has numerous enhancements, the most useful being variables and nested selectors.

You need to run it through a pre-processor to convert it to CSS before shipping it to the client.

I've been a hardcore CSS developer for many years now, but since forcing myself to do a project in SCSS, I now won't use anything else.

Not PHP I'm afraid, but Zope and Plone use something similar to SASS called DTML to achieve this. It's incredibly useful in CMS's.

Upfront Systems has a good example of its use in Plone.

If you have Ruby on your system you can do this:

http://unixgods.org/~tilo/Ruby/Using_Variables_in_CSS_Files_with_Ruby_on_Rails.html

This was made for Rails, but see below for how to modify it to run it stand alone.

You could use this method independently from Rails, by writing a small Ruby wrapper script which works in conjunction with site_settings.rb and takes your CSS-paths into account, and which you can call every time you want to re-generate your CSS (e.g. during site startup)

You can run Ruby on pretty much any operating system, so this should be fairly platform independent.

e.g. wrapper: generate_CSS.rb (run this script whenever you need to generate your CSS)

#/usr/bin/ruby  # preferably Ruby 1.9.2 or higher
require './site_settings.rb' # assuming your site_settings file is on the same level 

CSS_IN_PATH  = File.join( PATH-TO-YOUR-PROJECT, 'css-input-files')
CSS_OUT_PATH = File.join( PATH-TO-YOUR-PROJECT, 'static' , 'stylesheets' ) 

Site.generate_CSS_files( CSS_IN_PATH , CSS_OUT_PATH )

the generate_CSS_files method in site_settings.rb then needs to be modified like this:

module Site
#   ... see above link for complete contents
 
  # Module Method which generates an OUTPUT CSS file *.css for each INPUT CSS file *.css.in we find in our CSS directory
  # replacing any mention of Color Constants , e.g. #SomeColor# , with the corresponding color code defined in Site::Color
  #
  # We will only generate CSS files if they are deleted or the input file is newer / modified
  #
  def self.generate_CSS_files(input_path = File.join( Rails.root.to_s , 'public' ,'stylesheets') , 
                              output_path = File.join( Rails.root.to_s , 'public' ,'stylesheets'))
    # assuming all your CSS files live under "./public/stylesheets"
    Dir.glob( File.join( input_path, '*.css.in') ).each do |filename_in|
      filename_out = File.join( output_path , File.basename( filename_in.sub(/.in$/, '') ))

      # if the output CSS file doesn't exist, or the the input CSS file is newer than the output CSS file:
      if (! File.exists?(filename_out)) || (File.stat( filename_in ).mtime > File.stat( filename_out ).mtime)
        # in this case, we'll need to create the output CSS file fresh:
        puts " processing #{filename_in}\n --> generating #{filename_out}"
      
        out_file = File.open( filename_out, 'w' )
        File.open( filename_in , 'r' ).each do |line|
          if line =~ /^\s*\/\*/ || line =~ /^\s+$/             # ignore empty lines, and lines starting with a comment
            out_file.print(line)
            next
          end
          while  line =~ /#(\w+)#/  do                         # substitute all the constants in each line
            line.sub!( /#\w+#/ , Site::Color.const_get( $1 ) ) # with the color the constant defines
          end
          out_file.print(line)
        end
        out_file.close
      end # if ..
    end
  end # def self.generate_CSS_files
  
end # module Site

If you write the css file as an xsl template, you could read color values from a simple xml file. Then create the css with an xslt processor.

colors.xml:

<?xml version="1.0"?>
<colors>
    <background>#ccc</background>
</colors>

styles.xsl:

<?xml version="1.0"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output method="text" version="1.0" encoding="iso-8859-1"/>
    <xsl:template match="/">body {
    background-color: <xsl:value-of select="/colors/background" />;
}
</xsl:template>
</xsl:stylesheet>

Command to render css: xsltproc -o styles.css styles.xsl colors.xml

styles.css:

body {
    background-color: #ccc;
}

It’s not possible with CSS alone.

You can do it with JavaScript and LESS using less.js, which will render LESS variables into CSS live, but it’s for development only and adds too much overhead for real-life use.

The closest you can come with CSS is to use an attribute substring selector like this:

[id*="colvar-"] {
	color: #f0c69b;
}

and set the ids of all your elements that you want to be adjusted to names starting with colvar-, such as colvar-header. Then when you change the color, all the ID styles are updated. That’s as close as you can get with CSS alone.