attr

Summary

The attr() CSS function is used to retrieve the value of an attribute of the selected element and use it in the style sheet. It can be used on pseudo-elements too and, in this case, the value of the attribute on the pseudo-element's originated element is returned.

The attr() function can be used with any CSS property, but support for properties other than content is experimental.

Syntax

/* Simple usage */
attr(data-count);
attr(title);

/* With type */
attr(src url);
attr(data-count number);
attr(data-width px);

/* With fallback */
attr(data-count number, 0);
attr(src url, '');
attr(data-width px, inherit);
attr(data-something, 'default');

Values

attribute-name

Is the name of an attribute on the HTML element referenced in the CSS.

<type-or-unit>

Is a keyword representing either the type of the attribute's value, or its unit, as in HTML some attributes have implicit units. If the use of <type-or-unit> as a value for the given attribute is invalid, the attr() expression will be invalid too. If omitted, it defaults to string. The list of valid values are:

Keyword	Associated type	Comment	Default value
string	<string>	The attribute value is treated as a CSS <string>.  It is NOT reparsed, and in particular the characters are used as-is instead of CSS escapes being turned into different characters.	An empty string
color	<color>	The attribute value is parsed as a hash (3- or 6-value hash) or a keyword. It must be a valid CSS <string> value. Leading and trailing spaces are stripped.	currentColor
url	<uri>	The attribute value is parsed as a string that is used inside a CSS url()function. Relative URL are resolved relatively to the original document, not relatively to the style sheet. Leading and trailing spaces are stripped.	The url about:invalid that points to a non-existent document with a generic error condition.
integer	<integer>	The attribute value is parsed as a CSS <integer>. If it is not valid, that is not an integer or out of the range accepted by the CSS property, the default value is used. Leading and trailing spaces are stripped.	0, or, if 0 is not a valid value for the property, the property's minimum value.
number	<number>	The attribute value is parsed as a CSS <number>. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used. Leading and trailing spaces are stripped.	0, or, if 0 is not a valid value for the property, the property's minimum value.
length	<length>	The attribute value is parsed as a CSS <length> dimension, that is including the unit (e.g. 12.5em). If it is not valid, that is not a length or out of the range accepted by the CSS property, the default value is used. If the given unit is a relative length, attr()computes it to an absolute length. Leading and trailing spaces are stripped.	0, or, if 0 is not a valid value for the property, the property's minimum value.
em, ex, px, rem, vw, vh, vmin, vmax, mm, cm, in, pt, or pc	<length>	The attribute value is parsed as a CSS <number>, that is without the unit (e.g. 12.5), and interpreted as a <length> with the specified unit. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used. If the given unit is a relative length, attr()computes it to an absolute length. Leading and trailing spaces are stripped.	0, or, if 0 is not a valid value for the property, the property's minimum value.
angle	<angle>	The attribute value is parsed as a CSS <angle> dimension, that is including the unit (e.g. 30.5deg). If it is not valid, that is not an angle or out of the range accepted by the CSS property, the default value is used. Leading and trailing spaces are stripped.	0deg, or, if 0deg is not a valid value for the property, the property's minimum value.
deg, grad, rad	<angle>	The attribute value is parsed as a CSS <number>, that is without the unit (e.g. 12.5), and interpreted as an <angle> with the specified unit. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used. Leading and trailing spaces are stripped.	0deg, or, if 0deg is not a valid value for the property, the property's minimum value.
time	<time>	The attribute value is parsed as a CSS <time> dimension, that is including the unit (e.g. 30.5ms). If it is not valid, that is not a time or out of the range accepted by the CSS property, the default value is used. Leading and trailing spaces are stripped.	0s, or, if 0s is not a valid value for the property, the property's minimum value.
s, ms	<time>	The attribute value is parsed as a CSS <number>, that is without the unit (e.g. 12.5), and interpreted as an<time> with the specified unit. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used. Leading and trailing spaces are stripped.	0s, or, if 0s is not a valid value for the property, the property's minimum value.
frequency	<frequency>	The attribute value is parsed as a CSS <frequency> dimension, that is including the unit (e.g. 30.5kHz). If it is not valid, that is not a frequency or out of the range accepted by the CSS property, the default value is used.	0Hz, or, if 0Hz is not a valid value for the property, the property's minimum value.
Hz, kHz	<frequency>	The attribute value is parsed as a CSS <number>, that is without the unit (e.g. 12.5), and interpreted as a <frequency> with the specified unit. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used. Leading and trailing spaces are stripped.	0Hz, or, if 0Hz is not a valid value for the property, the property's minimum value.
%	<percentage>	The attribute value is parsed as a CSS <number>, that is without the unit (e.g. 12.5), and interpreted as a <percentage>. If it is not valid, that is not a number or out of the range accepted by the CSS property, the default value is used. If the given value is used as a length, attr()computes it to an absolute length. Leading and trailing spaces are stripped.	0%, or, if 0% is not a valid value for the property, the property's minimum value.

<fallback>

The value to be used if the associated attribute is missing or contains an invalid value. The fallback value must be valid where attr() is used, even if it is not used, and must not contain another attr() expression. If attr() is not the sole component value of a property, its <fallback> value must be of the type defined by <type-or-unit>. If not set, CSS will use the default value defined for each <type-or-unit>.

Formal syntax

attr( <attr-name> <type-or-unit>? [, <attr-fallback> ]? )
where 
<type-or-unit> = string | integer | color | url | integer | number | length | angle | time | frequency | em | ex | px | rem | vw | vh | vmin | vmax | mm | cm | in | pt | pc | deg | grad | rad | ms | s | Hz | kHz | %

Examples

p::before {
  content: attr(data-foo) " ";
}

<p data-foo="hello">world</p>

Result

Specifications

Browser compatibility

[1] See bug 435426.

[2] See Chromium bug 246571