body {background-color: #FFFFDD} (pale yellow).

HTML/CSS Test Page

h2 {color: green}

h2 + h2 {color: red}

h2 + h3 {color: blue}

All the actual style information for this page is in the <style> tag in the <head>; it is repeated in the body text by way of explanation, but it's only text--it doesn't do anything there.
Except, that is, in this table,
where the colors are defined in-line.

body S+ h3 {color: aqua} does not appear to work

Here are b.important {font-size: 24pt} and also b.trivial {font-size: 8}, as well as b#important {font-size: 20}.

This document uses p, div {padding-bottom: 8px}.

This is a <div class="one"> paragraph (where div.one {color="purple"}); and it has a <span class="one"> section in it, where span.one {color="blue"}.
And this is a fancy font, defined by span.fancy {font-size: 36; font-family: "NoSuchFont", "FrenchScript", "Comic Sans MS", "fantasy"}.
Here is a paragraph that should be right-justified (rather than the usual left-justified) because it uses <div class="right">, which is defined as div.right {text-align: right; font: bold small-caps 12pt/20pt sans-serif}; this is also an example of abbreviations (12pt/20pt refers to font size and leading, that is, line-height).
Let's try for some bright colors with span.colors {color: #F00; background-color: rgb(0, 0, 255)}.

If this one works, it's a doozy. We've got both div.borders {text-indent: 5em; padding: 8px} and div.borders {border-width: 12px; border-style: groove; border-color: red} defined on this one. And inside it, we have a i#borders {border-width: thick; border-style: double; border-color: green} italicized chunk, and maybe even an unbordered span#secret {border-style: none} chunk.
You should try this in different browsers. Opera seems to do a pretty good job, but both IE and Firefox get some things wrong.