Why doesn't CSS hover work on table rows when the cells inside the rows have class names?

Question

I am stuck with this problem so any help would be appreciated. I have a table with several rows. Each cell within the row belongs to a certain class. I use these class names to

Answer 1

I think the td background-color overwrites the tr background-color. The solution given by @Nick Craver is the good one.
You must change cells background-color not the row background-color.

tr:hover td {
   ...
}