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opacity

The opacity property in CSS specifies how transparent an element is.

Basic use:

div {
  opacity: 0.5;
}

Opacity has a default initial value of 1 (100% opaque). Opacity is not inherited, but because the parent has opacity that applies to everything within it. You cannot make a child element less transparent than the parent, without some trickery. Values are a number from 0 to 1 representing the opacity of the channel (the "alpha" channel). When an element has a value of 0 the element is completely invisible; a value of 1 is completely opaque (solid).

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IE Compatibility

If you want opacity to work in all versions of IE, the order should be as follows:

.opaque {
  /* Theoretically for IE 8 & 9 (more valid) */
  /* ...but not required as filter works too */
  /* should come BEFORE filter */
  -ms-filter:"progid:DXImageTransform.Microsoft.Alpha(Opacity=50)"; // IE8

  /* This works in IE 8 & 9 too */
  /* ... but also 5, 6, 7 */
  filter: alpha(opacity=50); // IE 5-7
  
  /* Modern Browsers */
  opacity: 0.5;
}

If you don’t use this order, IE8-as-IE7 doesn’t apply the opacity, although IE8 and a pure IE7 do.

Note on Stacking Contexts

If an element with opacity and a value less than 1 is positioned, the z-index property applies as described in CSS2.1, except that the auto value is treated as 0 since a new stacking context is always created.

Opacity can be used as an alternative to the visibility property: visibility: hidden; is just like opacity: 0;.

Related Properties

Other Resources

Browser Support

Chrome Safari Firefox Opera IE Android iOS
24+ 5.1+ 19+ 12.1+ 9+ 2.1+ 3.2+
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