Depends on what your target browsers are. In newer ones it's as simple as:
-moz-box-shadow: 0 0 5px #fff;
-webkit-box-shadow: 0 0 5px #fff;
box-shadow: 0 0 5px #fff;
For older browsers you have to implement workarounds, e.g., based on this example, but you will most probably need extra mark-up.