well, I often refer to css as akin to a private in the Army- it will do EXACTLY what you LAST told it to do.. sorta like this:
will give you a margin of 0px all around your element. But:
will give you what you are looking for, 0px around everything except the top, which will be 5px. This causes lots of folks issues.
As far as yours, you would be defining the style in the call, on your theme- but your theme is going to use an external stylesheet to control the layout.. which comes last? The stylesheet rules or the call rules? debatable I would reckon... But I think the HTML or PHP call trumps the external stylesheet... but if you are calling something via WP function, that function may have embedded a tag which WILL look for external styles defined- so it would look like this:
<h5 style="color:#ccc;"><h5> your text which external css got a hold of </h5></h5>
I don't know if that is the case, I am just speculating it could be the cause... It is something I think I will play with to learn more about..