In Firebug, how to tell what is overriding a style?

Question

I have this css:

fieldset li {  
padding-bottom: 0em;  
}  

However, it wasn\'t behaving properly, and using firebug, I see that style has

Answer 1

If a CSS rule is overridden although it is the top-most rule of that property, look further down for a rule that has the !important override set.