How to apply box-shadow on all four sides?

It’s because of x and y offset. Try this:

-webkit-box-shadow: 0 0 10px #fff;
        box-shadow: 0 0 10px #fff;

edit (year later..): Made the answer more cross-browser, as requested in comments 🙂

btw: there are many css3 generator nowadays..
css3.me, css3maker, css3generator etc…