PunBB Custom Border Help

I want to add a border on my forum but i don't know the code. I searched the forum for answers but i can't find any working code for punbb.
Can i use this as my border? http://ptpmp.net/forum/Themes/citiez_20rc5/images/custom/main_border.png ?

This code doesn't seem to work on punBB

Code:

#main_border_r {
    background: transparent url("../images/custom/main_border.png") repeat-y scroll 100% 0px;
        background-color: transparent;
        background-image: url("../images/custom/main_border.png");
        background-repeat: repeat-y;
        background-attachment: scroll;
        background-position: 100% 0px;
        background-clip: border-box;
        background-origin: padding-box;
        background-size: auto auto;
    padding: 0px 8px;
        padding-top: 0px;
        padding-right: 8px;
        padding-bottom: 0px;
        padding-left: 8px;
}

which code does this belong?