Reducing the width of div moves to left side in css

Reducing the width of div moves to left side in css

Here is the
http://jsfiddle.net/vicky081/jmGwX/5/ I want to change the width of the
div which is now 100% when i change the width to 50% the div appear left
side. How can i make that div as center by this when i reduce the size of
the div it appear from the center is it possible? I know the width of the
div is 100% then it appear like from left 0 to right 100 if i change the
width to 50 also it appear from left to 50% right Is there is a way to
show it from center when i change the width it appear both for example: if
i reduce the width of the div is 50% then it appear like 25% from center
of left and 25% center of right
Here is the code CSS:
.notify {
background: #FFFFFF;
width:50%;
position: relative;
margin:-13px 0px 0px -5px;
padding: 2px 0px 0px 0px;
border-bottom:2px solid #CC0000;
box-shadow: 0px 4px 5px #AAAAAA;
font-size:14px;
font-family: 'Lato Regular', Arial;
text-transform:uppercase;
text-align:center;
}