Example: HTML versus CSS

Let's suppose you want to say something like:

Mary had a little lamb.

That's pretty straightforward, isn't it? You've made your statement (presented your content), and there it is. But what if you wanted to emphasize a part of that statement, say by using some bold letters...

Mary had a little lamb.

...or maybe by using bold letters in one place and italicizing others...

Mary had a little lamb.

... or even all that plus some color...

Mary had a little lamb.

You can see that the HTML (the content) is the the same in all four statements, but the style (or presentation - CSS) is different in each of them.