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declaration-block-no-duplicate-properties

Disallow duplicate properties within declaration blocks.

a { color: pink; color: orange; }
/** ↑ ↑
* These duplicated properties */

This rule ignores variables ($sass, @less, --custom-property).

Options

true

The following patterns are considered problems:

a { color: pink; color: orange; }
a { color: pink; background: orange; color: orange }

The following patterns are not considered problems:

a { color: pink; }
a { color: pink; background: orange; }

Optional secondary options

ignore: ["consecutive-duplicates"]

Ignore consecutive duplicated properties.

They can prove to be useful fallbacks for older browsers.

The following patterns are considered problems:

p {
font-size: 16px;
font-weight: 400;
font-size: 1rem;
}

The following patterns are not considered problems:

p {
font-size: 16px;
font-size: 1rem;
font-weight: 400;
}

ignore: ["consecutive-duplicates-with-different-values"]

Ignore consecutive duplicated properties with different values.

Including duplicate properties (fallbacks) is useful to deal with older browsers support for CSS properties. E.g. using px units when rem isn't available.

The following patterns are considered problems:

/* properties with the same value */
p {
font-size: 16px;
font-size: 16px;
font-weight: 400;
}
/* nonconsecutive duplicates */
p {
font-size: 16px;
font-weight: 400;
font-size: 1rem;
}

The following patterns are not considered problems:

p {
font-size: 16px;
font-size: 1rem;
font-weight: 400;
}

ignore: ["consecutive-duplicates-with-same-prefixless-values"]

Ignore consecutive duplicated properties with identical values, when ignoring their prefix.

This option is useful to deal with draft CSS values while still being future proof. E.g. using fit-content and -moz-fit-content.

The following patterns are considered problems:

/* nonconsecutive duplicates */
p {
width: fit-content;
height: 32px;
width: -moz-fit-content;
}
/* properties with different prefixless values */
p {
width: -moz-fit-content;
width: 100%;
}

The following patterns are not considered problems:

p {
width: -moz-fit-content;
width: fit-content;
}

ignoreProperties: ["/regex/", "non-regex"]

Ignore duplicates of specific properties.

Given:

["color", "/background-/"]

The following patterns are considered problems:

a { color: pink; background: orange; background: white; }
a { background: orange; color: pink; background: white; }

The following patterns are not considered problems:

a { color: pink; color: orange; background-color: orange; background-color: white; }
a { color: pink; background-color: orange; color: orange; background-color: white; }