CSS coding guidelines

Our CSS is written in Sass, using the SCSS syntax.


The SCSS source files are compiled to CSS using the [gulp](http://gulpjs.com/) build system. This requires [node.js](http://nodejs.org) to run. To install the libraries required for compiling the SCSS, run the following from the Wagtail repository root:

$ npm install

To compile the assets, run:

$ npm run build

Alternatively, the SCSS files can be monitored, automatically recompiling when any changes are observed, by running:

$ npm start


  • Use soft-tabs with a four space indent. Spaces are the only way to guarantee code renders the same in any person’s environment.
  • Put spaces after : in property declarations.
  • Put spaces before { in rule declarations.
  • Put line breaks between rulesets.
  • When grouping selectors, keep individual selectors to a single line.
  • Place closing braces of declaration blocks on a new line.
  • Each declaration should appear on its own line for more accurate error reporting.
  • Add a newline at the end of your .scss files.
  • Strip trailing whitespace from your rules.


  • Use hex color codes #000 unless using rgba() in raw CSS (SCSS’ rgba() function is overloaded to accept hex colors as a param, e.g., rgba(#000, .5)).
  • Use // for comment blocks (instead of /* */).
  • Use single quotes for string values background: url('my/image.png') or content: 'moose'
  • Avoid specifying units for zero values, e.g., margin: 0; instead of margin: 0px;.
  • Strive to limit use of shorthand declarations to instances where you must explicitly set all the available values.

Sass imports

Leave off underscores and file extensions in includes:

// Bad
@import 'components/_widget.scss'

// Better
@import 'components/widget'

Pixels vs. ems

Use rems for font-size, because they offer absolute control over text. Additionally, unit-less line-height is preferred because it does not inherit a percentage value of its parent element, but instead is based on a multiplier of the font-size.

Specificity (classes vs. ids)

Always use classes instead of IDs in CSS code. IDs are overly specific and lead to duplication of CSS.

When styling a component, start with an element + class namespace, prefer direct descendant selectors by default, and use as little specificity as possible. Here is a good example:

<ul class="category-list">
    <li class="item">Category 1</li>
    <li class="item">Category 2</li>
    <li class="item">Category 3</li>
.category-list { // element + class namespace

    // Direct descendant selector > for list items
    > li {
        list-style-type: disc;

    // Minimal specificity for all links
    a {
        color: #f00;

Class naming conventions

Never reference js- prefixed class names from CSS files. js- are used exclusively from JS files.

Use the SMACSS is- prefix for state rules that are shared between CSS and JS.


As a rule of thumb, avoid unnecessary nesting in SCSS. At most, aim for three levels. If you cannot help it, step back and rethink your overall strategy (either the specificity needed, or the layout of the nesting).


Here are some good examples that apply the above guidelines:

// Example of good basic formatting practices
.styleguide-format {
    color: #000;
    background-color: rgba(0, 0, 0, .5);
    border: 1px solid #0f0;

// Example of individual selectors getting their own lines (for error reporting)
.get-new-lines {
    display: block;

// Avoid unnecessary shorthand declarations
.not-so-good {
    margin: 0 0 20px;
.good {
    margin-bottom: 20px;

Vendor prefixes

Line up your vendor prefixes.

// Example of good prefix formatting practices
.styleguide-format {
    -webkit-transition: opacity 0.2s ease-out;
       -moz-transition: opacity 0.2s ease-out;
        -ms-transition: opacity 0.2s ease-out;
         -o-transition: opacity 0.2s ease-out;
            transition: opacity 0.2s ease-out;

Don’t write vendor prefixes for border-radius, it’s pretty well supported.

If you’re unsure, you can always check support at caniuse

Linting SCSS

The guidelines are included in a .scss-lint.yml file so that you can check that your code conforms to the style guide.

Run the linter with scss-lint . from the wagtail project root. You’ll need to have the linter installed to do this. You can get it by running:

gem install scss-lint