This is a pseudo-class indicating a virtual component of a document -
the rendering viewport, including the scrollbar area. As such, its use is
limited and should not be combined with other elements in a selector.
Example
Ext/Doc: :viewport-scroll
{ border: thick solid blue }
(make a thick, solid, blue border around the viewport, including the
scrollbar-area.)
In-Line: NA
Browser Peculiarities
In Netscape 6, applying backgrounds and colors behaves the same as
:viewport or BODY as selectors. But, it gets interesting if you apply
borders, margin or other box properties - because the rendering box
in question isn't just the viewport, but it includes the scrollbar
area as well.
Applying 'margin' properties with this pseudo-class seems to only
apply it to the region to the right of the scrollbar area on the
right-hand side of the viewport. Padding seems to create odd effects too.