Hash sign in front of property name - CSS browser hack?

Question

This is the css part I'm working on:

.center-part-3 { #position: relative; #top: -50%; } 

I have never seen this type of use of a hash sign. What is this for?

Answer 1

Theoretically, this hack IE7 :

But here you have an exhaustive list of browsers that fails or passes this hack . IE is not in the list (neither in the list that passed or failed), but also adds other browsers to the crash list.

Answer 2

Like all CSS hacks, it abuses that some browsers will use the rule, while others will not. Here is a small link .