CSS absolute positioning

We do not have relative positioning in CSS. what I mean by that is the position:relative in css means the item is a reference for others. for example if you have an outer div with the follwing css:

#outerDiv {

    width: 770px;

    margin: 0 auto;

    position: relative;

    background: #fff url(../images/banner.jpg) no-repeat;

}

the above div will be in middle of page and it will be a start reference for other tags having absolute position.

#insideDiv{

    position: absolute;

    width:30px;
    background: #eee

    top: 0;

}

if in outerdiv we did not have  position:relative  the insidediv would start from body but when we have  position:relative it starts from outer div.

So Relative just means you are creating a reference for absolute positioning.