(1) A block can force itself to be shown over top of other
material by having a larger z-index.
(2) We won't see see all of this because it will be
behind the rest of the text with a
z-index of -100. This was text (2)
by the way.
(3) When there is a background color (i.e. not transparent)
overlapping blocks matter.
(4) Like many things in CSS, it is important to carefully
manage your use of z-index - especially when
you are using multiple CSS files from multiple sources and
when you are using JavaScript or something like JQuery
to tweak your markup.