There's no horizontal scroll bar with this page, because the outer div is exactly the right size, regardless of how you resize the window.
This technique can be used for anything where you want to set
used width of an element and you want margins, borders or
padding. Just set the width of the outer element to whatever you want
(123px or 80% or whatever) and then set the margin, borders and padding
on the inner element, while leaving the width of the inner
element unspecified (or as
auto, which is the same thing).