CSS jungle...

This time i need some help understanding this CSS-problem...

I want to put the PunBB part in a <div> wich runs from top to bottom of the browser window (see picture 1). Ive done the <div> and the css to make it do what i want, but when including the punbb variables into main.tpl (where ive put my layout changes) it stops looking like it used too (see picture 2).

Is there a css-guru here that might shed some light over this darkness?

Picture 1 (what it should look like)
http://www.riskaka.com/pics/punbb_error/right.png

Picture 2 (what it does look like)
http://www.riskaka.com/pics/punbb_error/wrong.png

this is the css code i use:

#sidebars {
    background-color: #669999;
    border-right-width: 1px;
    border-left-width: 1px;
    border-right-style: solid;
    border-left-style: solid;
    border-right-color: #000000;
    border-left-color: #000000;
    overflow: visible;
    visibility: visible;
    height: 100%;
    width: 80%;
    position: relative;
    left: 10%;
    bottom: 0px;
    top: 0px;
}