Center Horizontal with CSS

Demo

This div is centered.

HTML

<header>
    <div id="logo"></div>
</header>

CSS

header
{
    width: 100%;
    min-hight: 200px;
    position: relative;
}
header #logo
{
    position: absolute;
    left: 0;
    right: 0;
    margin: 0 auto;
}