css margin left, works in px but not in %

[babarian]

anybody knows why this code doesnt work:\[code\]#interieur{ display: inline-block; position: absolute; left:50%;}\[/code\]and this one does\[code\]#interieur{ display: inline-block; position: absolute; left:500px;}\[/code\]I'm working in PHP and the div "interieur" is inside an echo