How do I prevent my style from being overridden another style on a surrounding div?

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.