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Summary

The mask property in CSS allows users to alter the visibility of an item by either partially or fully hiding it. This is accomplished by either masking or clipping the image at specific points.

The mask shorthand also resets mask-border to its initial value. It is therefore recommended to use the mask shorthand rather than other shorthands or the individual properties to override any mask settings earlier in the cascade. This will ensure that mask-border has also been reset to allow the new styles to take effect.

Initial valueas each of the properties of the shorthand:
Applies toall elements; In SVG, it applies to container elements excluding the <defs> element and all graphics elements
Inheritedno
Percentagesas each of the properties of the shorthand:
Mediavisual
Computed valueas each of the properties of the shorthand:
Animation typeas each of the properties of the shorthand:
Canonical orderthe unique non-ambiguous order defined by the formal grammar
Creates stacking contextyes

Syntax

/* Keyword values */
mask: none;

/* Image values */
mask: url(mask.png);                       /* Pixel image used as mask */
mask: url(masks.svg#star);                 /* Element within SVG graphic used as mask */

/* Combined values */
mask: url(masks.svg#star) luminance;       /* Element within SVG graphic used as luminance mask */
mask: url(masks.svg#star) 40px 20px;       /* Element within SVG graphic used as mask positioned 40px from the top and 20px from the left */
mask: url(masks.svg#star) 0 0/50px 50px;   /* Element within SVG graphic used as mask with a width and height of 50px */
mask: url(masks.svg#star) repeat-x;        /* Element within SVG graphic used as horizontally repeated mask */
mask: url(masks.svg#star) stroke-box;      /* Element within SVG graphic used as mask extending to the box enclosed by the stroke */
mask: url(masks.svg#star) exclude;         /* Element within SVG graphic used as mask and combined with background using non-overlapping parts */

/* Global values */
mask: inherit;
mask: initial;
mask: unset;

Values

<mask-reference>
Sets the mask image source. See mask-image.
<masking-mode>
Sets the masking mode of the mask image. See mask-mode.
<position>
Sets the position of the mask image. See mask-position.
<bg-size>
Sets the size of the mask image. See mask-size.
<repeat-style>
Sets the repetition of the mask image. See mask-repeat.
<geometry-box>
If only one <geometry-box> value is given, it sets both mask-origin and mask-clip. If two <geometry-box> values are present, then the first sets mask-origin and the second mask-clip.
<geometry-box> | no-clip
Sets the area, which is affected by the mask image. See mask-clip.
<compositing-operator>
Sets the compositing operation used on the current mask layer. See mask-composite.

Formal syntax

<mask-layer>#

where
<mask-layer> = <mask-reference> <masking-mode>? || <position> [ / <bg-size> ]? || <repeat-style> || <geometry-box> || [ <geometry-box> | no-clip ] || <compositing-operator>

where
<mask-reference> = none | <image> | <mask-source>
<masking-mode> = alpha | luminance | match-source
<position> = [[ left | center | right | top | bottom | <length-percentage> ] | [ left | center | right | <length-percentage> ] [ top | center | bottom | <length-percentage> ] | [ center | [ left | right ] <length-percentage>? ] && [ center | [ top | bottom ] <length-percentage>? ]]
<bg-size> = [ <length-percentage> | auto ]{1,2} | cover | contain
<repeat-style> = repeat-x | repeat-y | [ repeat | space | round | no-repeat ]{1,2}
<geometry-box> = <shape-box> | fill-box | stroke-box | view-box
<compositing-operator> = add | subtract | intersect | exclude

where
<image> = <url> | <image()> | <image-set()> | <element()> | <cross-fade()> | <gradient>
<mask-source> = <url>
<length-percentage> = <length> | <percentage>
<shape-box> = <box> | margin-box

where
<image()> = image( [ [ <image> | <string> ]? , <color>? ]! )
<image-set()> = image-set( <image-set-option># )
<element()> = element( <id-selector> )
<cross-fade()> = cross-fade( <cf-mixing-image> , <cf-final-image>? )
<gradient> = <linear-gradient()> | <repeating-linear-gradient()> | <radial-gradient()> | <repeating-radial-gradient()>
<box> = border-box | padding-box | content-box

where
<color> = <rgb()> | <rgba()> | <hsl()> | <hsla()> | <hex-color> | <named-color> | currentcolor | <deprecated-system-color>
<image-set-option> = [ <image> | <string> ] <resolution>
<cf-mixing-image> = <percentage>? && <image>
<cf-final-image> = <image> | <color>
<linear-gradient()> = linear-gradient( [ <angle> | to <side-or-corner> ]? , <color-stop-list> )
<repeating-linear-gradient()> = repeating-linear-gradient( [ <angle> | to <side-or-corner> ]? , <color-stop-list> )
<radial-gradient()> = radial-gradient( [ <ending-shape> || <size> ]? [ at <position> ]? , <color-stop-list> )
<repeating-radial-gradient()> = repeating-radial-gradient( [ <ending-shape> || <size> ]? [ at <position> ]? , <color-stop-list> )

where
<rgb()> = rgb( <rgb-component>#{3} )
<rgba()> = rgba( <rgb-component>#{3} , <alpha-value> )
<hsl()> = hsl( <hue>, <percentage>, <percentage> )
<hsla()> = hsla( <hue>, <percentage>, <percentage>, <alpha-value> )
<named-color> = transparent | aliceblue | antiquewhite | aqua | aquamarine | azure | beige | bisque | black | blanchedalmond | blue | blueviolet | brown | burlywood | cadetblue | chartreuse | chocolate | coral | cornflowerblue | cornsilk | crimson | cyan | darkblue | darkcyan | darkgoldenrod | darkgray | darkgreen | darkgrey | darkkhaki | darkmagenta | darkolivegreen | darkorange | darkorchid | darkred | darksalmon | darkseagreen | darkslateblue | darkslategray | darkslategrey | darkturquoise | darkviolet | deeppink | deepskyblue | dimgray | dimgrey | dodgerblue | firebrick | floralwhite | forestgreen | fuchsia | gainsboro | ghostwhite | gold | goldenrod | gray | green | greenyellow | grey | honeydew | hotpink | indianred | indigo | ivory | khaki | lavender | lavenderblush | lawngreen | lemonchiffon | lightblue | lightcoral | lightcyan | lightgoldenrodyellow | lightgray | lightgreen | lightgrey | lightpink | lightsalmon | lightseagreen | lightskyblue | lightslategray | lightslategrey | lightsteelblue | lightyellow | lime | limegreen | linen | magenta | maroon | mediumaquamarine | mediumblue | mediumorchid | mediumpurple | mediumseagreen | mediumslateblue | mediumspringgreen | mediumturquoise | mediumvioletred | midnightblue | mintcream | mistyrose | moccasin | navajowhite | navy | oldlace | olive | olivedrab | orange | orangered | orchid | palegoldenrod | palegreen | paleturquoise | palevioletred | papayawhip | peachpuff | peru | pink | plum | powderblue | purple | rebeccapurple | red | rosybrown | royalblue | saddlebrown | salmon | sandybrown | seagreen | seashell | sienna | silver | skyblue | slateblue | slategray | slategrey | snow | springgreen | steelblue | tan | teal | thistle | tomato | turquoise | violet | wheat | white | whitesmoke | yellow | yellowgreen
<deprecated-system-color> = ActiveBorder | ActiveCaption | AppWorkspace | Background | ButtonFace | ButtonHighlight | ButtonShadow | ButtonText | CaptionText | GrayText | Highlight | HighlightText | InactiveBorder | InactiveCaption | InactiveCaptionText | InfoBackground | InfoText | Menu | MenuText | Scrollbar | ThreeDDarkShadow | ThreeDFace | ThreeDHighlight | ThreeDLightShadow | ThreeDShadow | Window | WindowFrame | WindowText
<side-or-corner> = [ left | right ] || [ top | bottom ]
<color-stop-list> = <color-stop>{2,}
<ending-shape> = circle | ellipse
<size> = closest-side | farthest-side | closest-corner | farthest-corner | <length> | <length-percentage>{2}

where
<rgb-component> = <integer> | <percentage>
<alpha-value> = <number>
<hue> = <number>
<color-stop> = <color> <length-percentage>?

Examples

.target {
  mask: url(#c1) luminance;
}

.anothertarget {
  mask: url(resources.svg#c1) 50px 30px/10px 10px repeat-x exclude;
}

Specifications

Specification Status Comment
CSS Masking Level 1
The definition of 'mask' in that specification.
Candidate Recommendation Extends its usage to HTML elements.
Extends its syntax by making it a shorthand for the new mask-* properties defined in that specification.
Scalable Vector Graphics (SVG) 1.1 (Second Edition)
The definition of 'mask' in that specification.
Recommendation Initial definition

Browser compatibility

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support (for SVG, only setting the mask image) 1.0-webkit[1] (Yes) (Yes)[2] No support (Yes)-webkit[1] 4.0-webkit[3]
Applies to HTML Elements 1.0-webkit[1] ? 3.5 (1.9.1)[1] No support (Yes)-webkit[1] No support
Shorthand for mask-* properties 1.0-webkit[1] ? No support[4] No support (Yes)-webkit[1] No support
Feature Android Edge Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support (for SVG, only setting the mask image) 2.1-webkit (Yes) ? ? ? 3.2-webkit
Applies to HTML Elements ? ? ? ? ? ?
Shorthand for mask-* properties ? ? ? ? ? ?

[1] While the property itself is recognized, values applied to it don't have any effect. Though there is also a -webkit prefixed property, which can be used within SVG and HTML with a slightly different syntax (also allowing to set the non-standard -webkit-mask-attachment property).

[2] Starting in Gecko 10.0 (Firefox 10.0 / Thunderbird 10.0 / SeaMonkey 2.7), the default color space when handling masks is sRGB; previously, the default (and only supported color space) was linearRGB. This changes the appearance of mask effects, but brings Gecko into compliance with the second edition of the SVG 1.1 specification.

[3] While the property itself is recognized, values applied to it don't have any effect. Though there is also a -webkit prefixed property, which can be used within SVG and HTML with a slightly different syntax (also allowing to set the non-standard -webkit-mask-attachment property).

[4] The shorthand version of the property is currently not implemented. It is only available in Nightly and Dev Edition. See bug 1251161.

See also