APDivs use position:absolute in their css to position them a number of pixels from the edge of the browser window or, when properly used, a number of pixels from their relatively positioned parent element.
What you are actually looking for is position:fixed in css. Something like this...
position:fixed; /* since APDivs use position:absolute, you can't use them for this */
border:1px solid black;
You really should never use APDivs for a website layout. They will break your design depending on the viewer's browser settings and because of that, they have been removed from DWCC altogether. Position:absolute was never meant to be used as a layout method, the DW marketing department made a bad decision a while back and touted them as the perfect tool for new designers when in reality, they were pretty much the exact opposite.
Thanks for your detailed response. I'm very new to all this, so thanks for your patience in advance. Your statement about apdivs being removed from Dreamweaver is confusing—I'm working in DWCC now and apdivs are present in the layout palette.
I'm guessing you are actually using DWCS6 Cloud, not DWCC.
Go to Help > About Dreamweaver to check your version.
DWCS6 Cloud will show version 12.x and DWCC is version 13.x.
You are correct. Thank you for the information.