If you paint the backgrounds of html
and body
(giving each its own color), you’ll quickly notice that body
is being shifted down along with #container
, and #container
itself isn’t offset from the top of body
at all. This is a side effect of margin collapse, which I cover in detail here (although that answer describes a slightly different setup).
It’s this behavior that’s causing the scrollbar to appear, since you’ve declared body
to have 100% the height of html
. Note that the actual height of body
is unaffected, as margins are never included in height calculations.