[html] Using CSS to align a button bottom of the screen using relative positions

I need to position a button to the bottom of the screen. I need to use relative size and not absolute sizes, so it fits any screen size.

my CSS code:

position:relative;
left:20%;
right:20%;
bottom:5%;
top:60%;

This will work for any resolution,

button{
    position:absolute;
    bottom: 5%;
    right:20%;
}

http://jsfiddle.net/BUuSr/

<button style="position: absolute; left: 20%; right: 20%; bottom: 5%;"> Button </button>