Last updated February 21, 2013. Created on August 31, 2008.
Edited by JohnAlbin, sun, jhodgdon, aspilicious. Log in to edit this page.

DEPRECATED. These old draft standards have been superseded by the new CSS coding standards.
CSS coding standards issues
Drupal core "markup" component issues
Originating discussion
Initial proposal by Nick Lewis

Write valid CSS

All CSS code should be valid CSS, preferably to CSS 2.1. CSS 3.0 is acceptable too, provided the usage can be justified and the principles of graceful degradation / progressive enhancement are followed.

Concise terminology used in these standards:

selector {
  property: value;


Selectors should

  • be on a single line
  • have a space after the previous selector
  • end in an opening brace
  • be closed with a closing brace on a separate line without indentation
.book-navigation .page-next {
.book-navigation .page-previous {

.book-admin-form {

A blank line should be placed between each group, section, or block of multiple selectors of logically related styles.

Multiple selectors

Multiple selectors should each be on a single line, with no space after each comma:

#forum td.posts,
#forum td.topics,
#forum td.replies,
#forum td.pager {


All properties should be on the following line after the opening brace. Each property should:

  • be on its own line
  • be indented with two spaces, i.e., no tabs
  • have a single space after the property name and before the property value
  • end in a semi-colon
#forum .description {
  color: #efefef;
  font-size: 0.9em;
  margin: 0.5em;

Alphabetizing properties

Multiple properties should be listed in alphabetical order.


body {
  font-weight: normal;
  background: #000;
  font-family: helvetica, sans-serif;
  color: #FFF;


body {
  background: #000;
  color: #fff;
  font-family: helvetica, sans-serif;
  font-weight: normal;

Colors (especially hex values) are preferred to be in lowercase.

Properties with multiple values

Where properties can have multiple values, each value should be separated with a space.

  font-family: helvetica, sans-serif;

CSS3 properties, vendor prefixes, progressive enhancement

.progressive-enhancement {
  background: #000 none;
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#E5000000,endColorstr=#E5000000);
  background-color: rgba(0, 0, 0, 0.9);
.progressive-prefixes {
  background-color: #003471;
  background-image: -webkit-gradient(linear, left top, left bottom, from(#003471), to(#448CCB));
  background-image: -webkit-linear-gradient(top, #003471, #448CCB);
  background-image: -moz-linear-gradient(top, #003471, #448CCB);
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#00003471,endColorstr=#00448CCB);
  background-image: -ms-linear-gradient(top, #003471, #448CCB);
  background-image: -o-linear-gradient(top, #003471, #448CCB);
  background-image: linear-gradient(to bottom, #003471, #448CCB);
.vendor-prefixes {
  -moz-border-radius: 5px;
  -webkit-border-radius: 5px;
  border-radius: 5px;
  -moz-box-shadow: 0 3px 20px #000;
  filter: progid:DXImageTransform.Microsoft.Shadow(color=#000000, direction='180', strength='10');
  -ms-filter: "progid:DXImageTransform.Microsoft.Shadow(color=#000000, direction='180', strength='10')";
  -webkit-box-shadow: 0 3px 20px #000;
  box-shadow: 0 3px 20px #000;
  1. Order all properties alphabetically.
  2. Group vendor-specific with their respective standard CSS3 properties.
  3. Order vendor-specific properties alphabetically.
  4. Declare vendor-specific properties before standard properties.
  5. Declare potentially unsupported values after known to be supported values (progressive enhancement). (see CSS spec)

The special case of filter: should be grouped with ms-filter: and ordered before it (as in above example).

Vendor specific extensions may cause browser inconsistencies when declaring CSS3 before the standard has reached recommended status (a.k.a. finalized). Do not take for granted that a -vendor-xyz-property is and works the same as the final xyz-property.

It is recommended to avoid features of proprietary vendor extensions that are not supported by CSS3 standards.


In general, all comments should follow Drupal's common Doxygen formatting conventions to stay consistent with the rest of Drupal's code base. In areas, where those common conventions cannot be applied, we resort to the CSSDoc syntax (draft).

In line with PHP coding standards, block level documentation should be used as follows, to describe a section of code below the comment.

 * Documentation here.

Further details on the common comment syntax may be found in the Doxygen formatting conventions.

Shorter inline comments may be added after a property, preceded with a space:

  background-position: 0.2em 0.2em; /* LTR */
  padding-left: 2em; /* LTR */


Drupal supports conditional loading of CSS files with specific override rules for right-to-left languages. For a module, the override rule should be defined in a file named <module>-rtl.css (e.g., node-rtl.css). For a theme, the override rule should be defined in a file named style-rtl.css. The rule that is overridden should be commented in the default CSS rule.

From node-rtl.css:

#node-admin-buttons {
  clear: left;
  float: right;
  margin-left: 0;
  margin-right: 0.5em;

Rules in node.css which will be overridden if the rtl.css file is loaded:

#node-admin-buttons {
  clear: right; /* LTR */
  float: left; /* LTR */
  margin-left: 0.5em; /* LTR */

See also:

As a rule of thumb, add a /* LTR */ comment in your style:

  • when you use the keywords, 'left' or 'right' in a property, e.g. float: left;
  • where you use unequal margin, padding or borders on the sides of a box, e.g.,
    margin-left: 1em;
    margin-right: 2em;
  • where you specify the direction of the language, e.g. direction: ltr;

Looking for support? Visit the forums, or join #drupal-support in IRC.


hkirsman’s picture

I think grouping properties together by theyr similarity is more logical and intuitive. Consider these examples when you'd want to change change positioning.

/* Grouping properties by they similarity */
.foo {
  /* text  */
  color: red;
  font-size: 10px;
  font-weight: bold;
  /* Box model *
  position: absolute;
  bottom: 0;

/* Alphabetical ordering */
.foo {
  bottom: 0;
  color: red;
  font-size: 10px;
  font-weight: bold;
  position: absolute;

I think it's better to have position and bottom next to each rather putting one as the first property and other as the last.

It's like going to bookshop where books are categorized first by their topic and then by theyr name.

So lets start creating rules for this kind of grouping?

More read here:

RobW’s picture

A universally followed css organization style increases the likelihood of repeated patterns, which usually increases the level of gzip compression and frontend performance. The benefit of alphabetical order is that it's a rule that can be followed by everybody with no memorization, which is pretty essential in an open source project with hundreds of developers. Best of all worlds is if you use a css preprocessor you can keep your SASS or LESS properties ordered however you want and set the output to alphabetical.

Tim Jones Toronto’s picture


>which usually increases the level of gzip compression and frontend performance

Rob, just for fun:

1. When downloading the CSS sheet from the Drupal site theme (which in parts isn't alphabetical ordered *wink*), performing GZIP compression gives me a file size of 16,411 bytes.

2. When using this same file to ‘beautify’ into alphabetic ordering, GZIP gives a file size of 16,696 bytes.

So a purely random example but - it's basically 16K vs. 16K :)

In terms of layout, I can see the alphabetic order suiting certain people, whereas I prefer height and width together – purely based on logical arrangement.


Drupal / Multimedia Developer
SO OUT THERE Producer |

KrisBulman’s picture

I much prefer this (grouping by similarity) method, alphabetizing seems nothing more than prettifying code style, grouping by similarity is way more intuitive, and easier to get a sense of what the code is doing quickly.

bacon’s picture

If you use Vim, MacVim, the following might be helpful to converting uppercase CSS color hex values to lowercase.


And for alphabetizing, a couple of marked lines or a visual block can help you send your text to the Unix sort command:


fast women, pretty cars, sexy computers

bryanbraun’s picture

Thanks! Your Vim suggestions were really helpful for me. I also used one to find and replace all my tabs with spaces, which is a pain to do manually.

:%s/\t/  /gc

: bryan