Override Failure in CSS

[tinkerer]

I tried to Search for this but the Search feature seems broke. I am putting up a new 1.3.9e zen-cart for the first time. I have had quite a bit of success overriding whatever I wanted to. But, I've hit a dead-end trying to override the font color and background of the .productListing-rowheading and .productListing-heading classes. I have a copy of the original stylesheet.css in my override folder as well as a stylesheet_override.css file which I created which contains only the selectors I want to modify. I have made numerous overrides in this way without a problem. But, these two classes won't budge. Any ideas? Here is the section I'm trying to override:

TH.productListing-heading a:hover {
color: #FFFFFF;
background-color: #A0A040;
}

.productListing-rowheading {
background-color: #F00;
background-image: url(../images/tile_back.gif); /*TEST*/
height: 2em;
color: #0000FF;
}