CSS Styleguide

Table of Contents

1. Terminology
   • Rule Declaration
   • Selectors
   • Properties
2. CSS
   • Formatting
   • Comments
   • Naming Convention
   • ID Selectors
   • JavaScript hooks
   • Border
3. Translation
4. License

Terminology

Rule declaration

A “rule declaration” is the name given to a selector (or a group of selectors) with an accompanying group of properties. Here's an example:

.listing {
  font-size: 18px;
  line-height: 1.2;
}

Selectors

In a rule declaration, “selectors” are the bits that determine which elements in the DOM tree will be styled by the defined properties. Selectors can match HTML elements, as well as an element's class, ID, or any of its attributes. Here are some examples of selectors:

.my-element-class {
  /* ... */
}

[aria-hidden] {
  /* ... */
}

Properties

Finally, properties are what give the selected elements of a rule declaration their style. Properties are key-value pairs, and a rule declaration can contain one or more property declarations. Property declarations look like this:

/* some selector */ {
  background: #f1f1f1;
  color: #333;
}

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CSS

Formatting

• Use soft tabs (2 spaces) for indentation.
• Prefer dashes over camelCasing in class names.
• Do not use ID selectors.
• Do not use underscores, except to override an existing or external style.
• When using multiple selectors in a rule declaration, give each selector its own line.
• Put a space before the opening brace { in rule declarations.
• In properties, put a space after, but not before, the : character.
• Put closing braces } of rule declarations on a new line.
• Put blank lines between rule declarations.

Bad

.avatar{
    border-radius:50%;
    border:2px solid white; }
.no, .nope, .not_good {
    // ...
}
#lol-no {
  // ...
}

Good

.avatar {
  border-radius: 50%;
  border: 2px solid white;
}

.one,
.selector,
.per-line {
  // ...
}

Comments

• Prefer single-line comments to block comments.
• Prefer comments on their own line. Avoid end-of-line comments.
• Write detailed comments for code that isn't self-documenting:
  • Uses of z-index
  • Compatibility or browser-specific hacks

Naming Convention

The naming convention is a simplified version of BEM.

Example

<article class="listing-card featured">
  <h1 class="title">Adorable 2BR in the sunny Mission</h1>
  <div class="content">
    <p>Vestibulum id ligula porta felis euismod semper.</p>
  </div>
</article>

.listing-card { }
.listing-card.featured { }
.listing-card .title { }
.listing-card .content { }

• .listing-card is the “block” and represents the higher-level component
• .listing-card .title is an “element” and represents a descendant of .listing-card that helps compose the block as a whole.
• .listing-card.featured is a “modifier” and represents a different state or variation on the .listing-card block.

HTML tag names may be used instead of a class name to represent BEM-like elements.

Example

<article class="listing-card featured">
  <h1>Adorable 2BR in the sunny Mission</h1>
  <p>Vestibulum id ligula porta felis euismod semper.</p>
</article>

.listing-card { }
.listing-card.featured { }
.listing-card h1 { }
.listing-card p { }

ID selectors

While it is possible to select elements by ID in CSS, it should generally be considered an anti-pattern. ID selectors introduce an unnecessarily high level of specificity to your rule declarations, and they are not reusable.

For more on this subject, read CSS Wizardry's article on dealing with specificity.

JavaScript hooks

Avoid binding to the same class in both your CSS and JavaScript. Conflating the two often leads to, at a minimum, time wasted during refactoring when a developer must cross-reference each class they are changing, and at its worst, developers being afraid to make changes for fear of breaking functionality.

We recommend creating JavaScript-specific classes to bind to, prefixed with .js-:

<button class="btn btn-primary js-request-to-book">Request to Book</button>

Border

Use 0 instead of none to specify that a style has no border.

Bad

.foo {
  border: none;
}

Good

.foo {
  border: 0;
}

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License

(The MIT License)

Copyright (c) 2015 Airbnb

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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