Each of these windows shows
EXACTLY the same HTML file.
The
changes made to the CSS file produced three
very different presentations of that basic
content.
This is particularly useful
for changing the presentational aspects
of a site or group of pages.
You
typically only need to edit a single CSS
file, rather than editing all the code of
each HTML file.
This can also be beneficial
for localization, since typographic
approaches, colors, etc, may need to be
changed for different locales.
Making such changes in the CSS is much
easier than adapting the HTML.
"