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selector-pseudo-element-colon-notation

Specify single or double colon notation for applicable pseudo-element selectors.

    a::before {}
/**  ↑
 * This notation */

The :: notation was chosen for pseudo-elements to establish a discrimination between pseudo-classes (which subclass existing elements) and pseudo-elements (which are elements not represented in the document tree).

However, for compatibility with existing style sheets, user agents also accept the previous one-colon notation for pseudo-elements introduced in CSS levels 1 and 2 (namely, :first-line, :first-letter, :before and :after).

The fix option can automatically fix all of the problems reported by this rule.

Options​

string: "single"|"double"

"single"​

Applicable pseudo-elements must always use the single colon notation.

The following patterns are considered problems:

a::before { color: pink; }
a::after { color: pink; }
a::first-letter { color: pink; }
a::first-line { color: pink; }

The following patterns are not considered problems:

a:before { color: pink; }
a:after { color: pink; }
a:first-letter { color: pink; }
a:first-line { color: pink; }
input::placeholder { color: pink; }
li::marker { font-variant-numeric: tabular-nums; }

"double"​

Applicable pseudo-elements must always use the double colon notation.

The following patterns are considered problems:

a:before { color: pink; }
a:after { color: pink; }
a:first-letter { color: pink; }
a:first-line { color: pink; }

The following patterns are not considered problems:

a::before { color: pink; }
a::after { color: pink; }
a::first-letter { color: pink; }
a::first-line { color: pink; }
input::placeholder { color: pink; }
li::marker { font-variant-numeric: tabular-nums; }