CSS Coding Standards

CSS

Formatting

  • Use soft tabs (2 spaces) for indentation
  • Prefer dashes over camelCasing in class names.
  • Try to avoid using IDs as selectors
  • 0 values should be written as property: 0;, not property: 0px;
  • 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 1 blank line 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 line comments (// in Sass-land) 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

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;
}

Media Queries

  • Indentation by 2 spaces is required inside of a media query.
@media screen and (max-width: 768px) {
∙∙.selector-1 {
∙∙∙∙property: value;
∙∙}
}

SASS

Syntax

  • Use the .scss syntax, never the original .sass syntax
  • Order your regular CSS and @include declarations logically (see below)

Ordering of property declarations

  1. Property declarations List all standard property declarations, anything that isn’t an @include or a nested selector. 
    .btn-green {
  background: green;
  font-weight: bold;
  // ...
}
  2. @include declarations Grouping @include's at the end makes it easier to read the entire selector. 
    .btn-green {
  background: green;
  font-weight: bold;
  @include transition(background 0.5s ease);
}
  3. Nested selectors Nested selectors, if necessary, go last, and nothing goes after them. Add whitespace between your rule declarations and nested selectors, as well as between adjacent nested selectors. Apply the same guidelines as above to your nested selectors. 
    .btn {
background: green;
  font-weight: bold;
  @include transition(background 0.5s ease);

  .icon {
    margin-right: 10px;
  }
}

Variables

Prefer dash-cased variable names (e.g. $my-variable) over camelCased or snake_cased variable names. It is acceptable to prefix variable names that are intended to be used only within the same file with an underscore (e.g. $_my-variable).

Mixins

Mixins should be used to DRY up your code, add clarity, or abstract complexity–in much the same way as well-named functions. Mixins that accept no arguments can be useful for this, but note that if you are not compressing your payload (e.g. gzip), this may contribute to unnecessary code duplication in the resulting styles.

Nested selectors

Try to avoid nesting selectors more than three levels deep!

.page-container {
  .content {
    .profile {
      // STOP!
    }
  }
}

When selectors become this long, you’re likely writing CSS that is:

  • Strongly coupled to the HTML (fragile) —OR—
  • Overly specific (powerful) —OR—
  • Not reusable

Also, never nest ID selectors!

If you must use an ID selector in the first place (and you should really try not to), they should never be nested. If you find yourself doing this, you need to revisit your markup, or figure out why such strong specificity is needed. If you are writing well formed HTML and CSS, you should never need to do this.

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