Position:absolute and centering Options

[GunsNRachel]

I know when you have position: absolute and you put left: 50% it's supposed to center what you want to center.. but mine isn't? I'm confused. It puts it to the right instead of center.

Here's the code:

CODE

.heading{
width:700;
height:300;
background-color:ffffff;
border:0px;
border-color:000000;
border-style:solid;
position:absolute;
left:50%;
font-family:;
color:;
font-weight:normal;
font-size:;
letter-spacing:;}

[Jghelfi]

CODE

MARGIN-LEFT= GOES TO THE RIGHT
MARGIN-RIGHT= GOES TO THE LEFT
MARGIN-TOP= GOES TO THE BOTTOM
MARGIN-BOTTOM= GOES TO THE TOP

LEFT: 1-49% = GOES TO THE LEFT on a small number
LEFT: 50-100% = GOES TO THE RIGHT on a big number