I always set out my markup like this:
<div class="whatever">
<p>Paragraph text with <em>bold or whatever</em> within it.</p>
<ul>
<li>List item 1</li>
<li>List item 2</li>
</ul>
</div><!-- END OF WHATEVER -->
Then I just use descendent selectors for everything within the div,
.whatever p
.whatever ul
etc.
I zero out all the margins and padding right at the start of the CSS file.