Re: width:expression(document.body.clientWidth < 782? "780px" ?

[brandon]

It’s called a CSS expression. Google can give you a better explanation, but in short it’s a way to assign the result of a Javascript expression to a CSS attribute, rather than a static value.

EDIT: if you need a literal explanation of the code itself, it is stating:

if the body width is less than 782
then set the width to 780
else if the body width is greater than 1262
then set the width to 1260