To find out what .css documents are loaded and in what order:

1.View Source for the page.
2. Search for .css

All the .css files that are loaded will be found in order.

When overriding a css rule, you need to override the specific property within that rule:

In other words, when you have this:

td { 

   font-size: 1em;
   color:black;
   background-color:white;
}

In default.css, then when you put

td { 
   color:gold;
}

In a stylesheet that is loaded later, then only the color will be overridden, and the background-color will still be white with the font-size 1em.

To override the background-color property you need to explicity state what you want it to be in a .css file that is loaded later:

td { 
   color:gold;
   background-color:black;
}

Now you will have gold print on a black background and the font-size will still be 1em.

This is an over-simplification, but should explain why you might not be getting the change you want to take place.

Now the hard part is tracking down what stylesheet does what, but if you know the order, then as long as you explicitly define the styles you want, you will be "golden".