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SUIT CSS components

SUIT CSS is designed for styling reusable, composable components. The benefits are most apparent in a system that considers components to be the building blocks of your application.

Think of components as custom elements that enclose specific semantics, styling, and behaviour. For example, this Photo component and configuration:

<Photo src="photo.jpg" size="large" crop="circle">
  A photo of <a href="/barackobama">Barack Obama</a> in the Whitehouse.

could yield the following HTML:

<article class="Photo Photo--sizeLarge">
  <a class="Photo-crop Photo-crop--circle" href="photo.jpg">
    <span class="Photo-icon">
      <span class="Icon Icon--zoom"></span>
    <img class="Photo-img u-block" src="photo.jpg" alt="">
  <div class="Photo-caption u-textBreak">
    A photo of <a href="/barackobama">Barack Obama</a> in the Whitehouse.

SUIT CSS helps to partially isolate the CSS used in the Photo component's implementation. In doing so, it makes styling simpler by reducing the amount of styling entanglement between components, and prevents styles from leaking outside the component.

(Read about SUIT CSS's naming conventions.)

Component scope

The component's core class name (e.g., ComponentName) reserves a namespace that can only be used by that component. This can be enforced using with tools (e.g. suitcss-preprocessor or postcss-bem-linter) in your build process.

All selectors in a component file must start with the component's namespace. For example, a component called MyComponent could have the following CSS, where every selector starts with the string MyComponent.

/** @define MyComponent */

.MyComponent { /* ... */ }
.MyComponent--large { /* ... */ }
.MyComponent-title { /* ... */ }
.MyComponent-image { /* ... */ }
.MyComponent-text { /* ... */ }
.MyComponent-time { /* ... */ }

Each class provides a hook to style specific elements within the HTML definition.

<article class="MyComponent u-cf">
  <h1 class="MyComponent-title">{{title}}</h1>
  <img class="MyComponent-image" src="{{src}}" alt="">
  <p class="MyComponent-text">
    <span class="MyComponent-time">{{time}}</span>

Like classes, variables must also be scoped to their component by including the component name in the variable name:

/** @define MyComponent */

:root {
  --MyComponent-border-width: 5px;

.MyComponent {
  border-width: var(--MyComponent-border-width);
  /* ... */

This allows a theme to override the defaults if desired.

Avoid coupling or entangling components, even if that means the code is not as DRY as you think it should be. Isolation prevents avoidable complexity and is an important part of robust reuse.

One pattern, one component

Each component should implement a single part of the UI. Don't try to do too much.

Each component should have a dedicated CSS file. Ideally your component's files are grouped together in a dedicated directory.

Documenting implementation details

Components must document their implementation. The CSS comments for a component should seek to answer the following questions:

  • What is the intended presentation?
  • What are the modifiers and states?
  • What are the reasons for specific, opaque property values.
  • What are the known limitations?

Adapting to ancestral context

Most components should not set their own width, margin, and positioning. By authoring a component to be full-width or inline, it can better adapt to the dimensions of an ancestral context.

Styling dependencies

A component should not know about the implementation of its dependencies. The appearance of dependencies must be configured using the interface they provide.

Controlling dimensions, margins, position, and inheritable styles of a component can be done indirectly. Add a class to its root element, or wrap it in another element.

/* Excerpt */

.Excerpt {
  /* ... */

/* Attaches to a nested component */

.Excerpt-button {
  display: inline-block;
  margin-top: 20px;

/* Wraps a nested component */

.Excerpt-wrapButton {
  display: inline-block;
  margin-top: 20px;
<article class="Excerpt u-cf">
  {{! other implementation details }}

  <read-button class="Excerpt-button">Read more</read-button>

  <div class="Excerpt-wrapButton">
    <read-button>Read more</read-button>