Changing link color for one div class

I’m trying to keep the links blue on some parts of my site, but on other places black. I’m trying to do something like this:

.themargintext {
	a {color: #000000; }
	a:hover {color: #000000;}
}

using <div class="themargintext">

but it doesn’t work…
what am I doing wrong?

Thanks in advance