ID and Class combo in a Div layer

The part of my CSS is in the code below. Now i want to output my CSS in HTML as such:
<div id="grafiek" class="scale5">
Unfortunately however, this doesn't work.. Anyone a solution? Help will be very much apreciated!
1. #grafiek {
2. width: 710px;
3. height: 359px;
4. position: relative; }
5.
6. #grafiek .scale5 { background: url("../img/grafiek_bg_05.gif") no-repeat 0px 0px; }