shadow boxing with -moz-box-shadow

Another fun CSS3 feature that’s been implemented in Firefox 3.5 is box shadows. This feature allows the casting of a drop “shadow” from the frame of almost any arbitrary element.

As the CSS3 box shadow property is still a work in progress, however, it’s been implemented as -moz-box-shadow in Firefox. This is how Mozilla tests experimental properties in CSS, with property names prefaced with “-moz-“. When the specification is finalized, the property will be named “box-shadow.”

How it works

Applying a box shadow to an element is straightforward. The CSS3 standard allows as its value:

none |  [  ]*

where <shadow> is:

 = inset? && [ {2,4} && ? ]

The first two lengths are the horizontal and vertical offset of the shadow, respectively. The third length is the blur radius (compare that to the blur radius in in the text-shadow property). Finally the fourth length is the spread radius, allowing the shadow to grow (positive values) or shrink (negative values) compared to the size of the parent element.

The inset keyword is pretty well explained by the standard itself:

if present, [it] changes the drop shadow from an outer shadow (one that shadows the box onto the canvas, as if it were lifted above the canvas) to an inner shadow (one that shadows the canvas onto the box, as if the box were cut out of the canvas and shifted behind it).

But talk is cheap, let’s look at some examples.

To draw a simple shadow, just define an offset and a color, and off you go:

 -moz-box-shadow: 1px 1px 10px #00f;


simple box shadow

(Each of the examples in this article are live examples first, followed by a screen shot from Firefox 3.5 on OSX).

Similarly, you can draw an in-set shadow with the aforementioned keyword.

-moz-box-shadow: inset 1px 1px 10px #888;


inset box shadow

With the help of a spread radius, you can define smaller (or bigger) shadows than the element it is applied to:

-moz-box-shadow: 0px 20px 10px -10px #888;


box shadow with spread radius

If you want, you can also define multiple shadows by defining several shadows, separated by commas (courtesy of Markus Stange):

-moz-box-shadow: 0 0 20px black, 20px 15px 30px yellow, -20px 15px 30px lime, -20px -15px 30px blue, 20px -15px 30px red;


multiple box shadows

The different shadows blend into each other very smoothly, and as you may have noticed, the order in which they are defined does make a difference. As box-shadow is a CSS3 feature, Firefox 3.5 adheres to the CSS3 painting order. That means, the first specified shadow shows up on top, so keep that in mind when designing multiple shadows.

As a final example, I want to show you the combination of -moz-box-shadow with an RGBA color definition. RGBA is the same as RGB, but it adds an alpha-channel transparency to change the opacity of the color. Let’s make a black, un-blurred box shadow with an opacity of 50 percent, on a yellow background:

-moz-box-shadow: inset 5px 5px 0 rgba(0, 0, 0, .5);


box shadow with RGBA

As you can see, the yellow background is visible though the half-transparent shadow without further ado. This feature becomes particularly interesting when background images are involved, as you’ll be able to see them shining through the box shadow.

Cross-Browser Compatibility

As a newer, work-in-progress CSS3 property, box-shadow has not yet been widely adopted by browser makers.

  • Firefox 3.5 supports the feature as -moz-box-shadow, as well as multiple shadows, the inset keyword and a spread radius.
  • Safari/WebKit has gone down a similar route as Firefox by implementing the feature as -webkit-box-shadow. Multiple shadows are supported since version 4.0, while neither inset shadows nor the spread radius feature are supported yet in WebKit.
  • Finally, Opera and Microsoft Internet Explorer have not yet implemented the box shadow property, though in MSIE you may want to check out their proprietary DropShadow filter.

To achieve the biggest possible coverage, it is advisable to define all three, the -moz, -webkit, and standard CSS3 syntax in parallel. Applicable browsers will then pick and adhere to the ones they support. For example:

 -moz-box-shadow: 1px 1px 10px #00f;
 -webkit-box-shadow: 1px 1px 10px #00f;
 box-shadow: 1px 1px 10px #00f;

The good news is that the box-shadow property degrades gracefully on unsupported browsers. For example, all the examples above will look like plain and boring boxes with no shadow in MSIE.


The CSS3 box-shadow property is not yet as widely available in browsers (and therefore, to users) as, for example, the text-shadow property, but with the limited box shadow support of WebKit as well as the full support provided by Firefox 3.5 (as far as the current status of the feature draft is concerned), more and more users will be able to see some level of CSS box shadows.

As a web developer, you can therefore use the feature, confident that you are giving users with modern browsers an improved experience while not turning away users with older browsers.

Further resources


About Christopher Blizzard

Making the web better, one release at a time.

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  1. […] boxing with -moz-box-shadow This is another cross-post of an article I wrote for the blog. It shows off some of the fun stuff web developers can do […]

    June 12th, 2009 at 07:48

  2. Andy

    The best article on box-shadow I’ve seen on the Net.

    Thank you!

    June 12th, 2009 at 10:17

  3. […] 原文地址:shadow boxing with -moz-box-shadow 系列地址:颠覆网络35天 […]

    June 13th, 2009 at 00:46

  4. Frederic Wenzel

    Andy: Thanks, I am glad you liked it!

    June 15th, 2009 at 13:27

  5. […] 原文地址:shadow boxing with -moz-box-shadow 系列地址:颠覆网络35天 […]

    July 16th, 2009 at 01:06

  6. Kadir

    So, is there an easy way to display a shadow all around an object without repeating the box-shadow values for all 4 combinations of left-top, right-top etc.?

    December 25th, 2009 at 08:53

    1. Chad

      Yes you can. You can use the property above: -moz-box-shadow: 0px 20px 10px -10px #888; except instead of using a negative value for the fourth value you can make it positive. so it will look like this: -moz-box-shadow: 0px 20px 10px 10px #888;

      March 10th, 2010 at 09:07

      1. Kadir

        You also have to adjust the second value, otherwise it will look like a drop shadow: 0px 2px 10px 5px #888;

        March 15th, 2010 at 01:15

  7. Rui Falcao Costa


    January 6th, 2010 at 22:45

  8. Dan Pacey

    There’s only really one problem with box-shadow that I’ve found so far, and that’s the inability to set an opacity. Thus, any shadow created as #000 will be solid black. You can’t get around that by setting a lighter shade, as #ccc (for example) will appear as grey.

    So, to my design mind, the spec is incomplete and needs to account for such an option.

    May 13th, 2010 at 23:00

    1. Hakim Jonas Ghoula

      just use rgba for your color and you have transparency/opacity.

      For example: rgba(255,0,0,0.5) for red with 50% opacity

      November 7th, 2011 at 12:38

  9. Dan Pacey

    ah, guilty of not reading the whole article.. RGBA it is..

    May 13th, 2010 at 23:11

  10. […] instead!For more on box and text drop shadows, see:Take Your Design To The Next Level With CSS3Shadow boxing with -moz-box-shadow (relevant to non-Mozilla browsers to, from Trials: Box-Shadow And More […]

    May 16th, 2010 at 08:03

  11. orangorangan

    Thanks mate! nice reference, helps me alot :)

    October 26th, 2011 at 04:16

  12. Jewel Sarker

    Thanks for the solutions.

    April 26th, 2012 at 01:35

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