#zijkant_links {
    float: right;
    width: 10px;
    height: 100%;
    background-image: url(../images/witblok.gif);
    background-repeat: repeat;
}
#zijkant_rechts {
    float: left;
    width: 10px;
    height: 100%;
    background-image: url(../images/witblok.gif);
    background-repeat: repeat;
}