+3  A: 

You can throw the !important attribute on h3#issueHeader to force the browser to use that style

h3#issueHeader {
  color: blue !important;
}

However, it is only partially supported in IE6


Additionally, this should only be used as a last resort to the other solutions purposed. This is because if users of your website want to override your style, important becomes a useful tool for that. See this article: Don't use "!important"

Gavin Miller
Using the !important should only be a last resort. In this case, using a more specific selector works also.
Zack
@Zack - Thanks for that; I wasn't sure why it ought not to be used and did some googling. I've updated my answer accordingly.
Gavin Miller
+3  A: 

Try setting the selector as:

#Content h3#issueHeader {
    color: blue;
}

This should fix it.

Zack
+7  A: 

css gives more weight to elements with more selectors. So if you want #Content h3 not to override h3#issueHeader, give it another selector: e.g. #Content h3#issueHeader

If your h1...hx elements are meant to be generally #405679, set them to that without the #Content selector. Then override them with a more specific selector when you need to.

dnagirl
A: 

If id="issueHeader" is duplicated that could do it.

Vian Esterhuizen
I assume you mean if it is used in more than one style? Nope, I am not doing that. It is a very small stylesheet, so it's easy to check.
Jergason
A: 

You are having what's called CSS specificity. Here's a good writup (using starwars to boot), that explains the basics in terms of points and how to calculate what will cascade:

http://www.stuffandnonsense.co.uk/archives/css_specificity_wars.html

easement