The distinction between styling and layout is not quite "the'
issue when it comes to the question about style and meaning
generally. When style is spoken of in the context of these
matters, it is almost always meant to include both colouring,
sizing, and yes, positioning and layout too. And quite rightly
for most purposes.
An example of where layout is *obviously* crucial to meaning is a
tabular table. A table is a good example of where how something
is laid out determines its meaning. Once the basic
meaning-related layout is achieved (greatly assisted by built in
HTML table magic), there comes a time for the *stylistic*
enhancements like colours, types of fonts, border types,
background colours and so on. But it is not a clear cut thing. If
you look at a table of atomic elements, you will see that some of
the styling, especially background colours, play a more than mere
optional role. These more than optional roles are where the
blurring occurs. It is often quite difficult to think up ways to
communicate things without the help of style.
Another way to look at it is this. There is a built in styling
(and I am not talking about default values, paras indented just
so so) to writing html itself. The order of the paras are
important to meaning. You can't be messing too much with classes
and positioning here otherwise you will change the meaning of the
whole, or confuse it. A list, visually, naturally, goes down the
page in the order it is written. It does not change the meaning
much if it is put inline. But there are constraints, you can't do
just anything in css without affecting the meaning communicated.
There is sometimes more than a marriage of convenience between
HTML and CSS, sometimes it is a holy union. Its sanctity is only
obscured by the triviality of so much that passes by on the
internet.
The best thing that any author can do is create create html that
can stand on its own as much as possible. That means it will mean
as much as what the author wants to convey as possible on its
very own. Then it is time to hitch up. The marriage will be all
the more successful, the more independent the html is in the
first place. But that does not mean that the marriage *merely*
enhances the meaning.