Override CSS Rule

Hey Guys,

I have built a website using Dreamweaver & an external CSS style sheet, that controls the colours of my hyperlinks.  Things such as Hover, Colour when clicked and the colour of the link.  On one of the pages i want one link to be a different colour to the rest.  

I highlighted my text i want to be different, and clicked new CSS rule, i then selected Class, give it a new name of pdf_link, clicked OK & defined how i wanted it to look.  I then selected the style pdf_link to the highlighted text but it seems as if it is getting over ridden by my first CSS that exists for the other links on the page.  How can i fix this so i can make one link what ever colour i want and it is not defined by the original CSS rule.

My code says this: class="pdf_link">here</a>

Thanks