SVG drop shadow using css3

Here’s an example of applying dropshadow to some svg using the ‘filter’ property. If you want to control the opacity of the dropshadow have a look at this example. The slope attribute controls how much opacity to give to the dropshadow.

Relevant bits from the example:

<filter id="dropshadow" height="130%">
  <feGaussianBlur in="SourceAlpha" stdDeviation="3"/> <!-- stdDeviation is how much to blur -->
  <feOffset dx="2" dy="2" result="offsetblur"/> <!-- how much to offset -->
  <feComponentTransfer>
    <feFuncA type="linear" slope="0.5"/> <!-- slope is the opacity of the shadow -->
  </feComponentTransfer>
  <feMerge> 
    <feMergeNode/> <!-- this contains the offset blurred image -->
    <feMergeNode in="SourceGraphic"/> <!-- this contains the element that the filter is applied to -->
  </feMerge>
</filter>
<circle r="10" style="filter:url(#dropshadow)"/>

Box-shadow is defined to work on CSS boxes (read: rectangles), while svg is a bit more expressive than just rectangles. Read the SVG Primer to learn a bit more about what you can do with SVG filters.