CSS 3 box-shadow property, inset keyword and spread radius test case
As of now there is no longer a need to use -webkit- or -moz- prefixes.
Unprefixed box-shadow is widely supported.
If you want to support some older smartphones with default browsers based on WebKit you might consider to keep the -webkit-prefix for now.
This site's script no longer adds those prefixes. So you will not see shadows with browsers older than Firefox 4, Safari 5.1 or Chrome 10.
Currently (2012-07) only Gecko (Firefox), Safari, and Opera have a CSS standard
compliant implementation in regard to blur radius.
Other browsers (IE 9, Google Chrome) differ in blurring and might follow sooner or later.
Note that the two WebKit browsers Safari and Chrome behave different.
So you should use Firefox, Safari 5.1, or Opera 12 as reference to create a future-proof blurred box-shadow.
If the shadow color is omitted (as in the four examples below),
box-shadows are drawn in foreground color (text color).
Older WebKit browsers are buggy and ignore those shadows.
This bug is fixed in WebKit 536.7 and therefore fixed since Chrome 20 and Safari 6.