Wow! Thank you very much to both of you, MeltDown and charmedbytina2!

Thanks to MeltDown I discovered this great tool, Web Developer, which I didn't know it existed. I have no idea how I managed to do without it until now. Thanks to Web Developer, I quickly found that the color "bottom green bar" in question is handled in:

.leftBoxContainer, .rightBoxContainer {
margin: 0em;
border: 1px solid #9a9a9a;
border-bottom: 5px solid #336633;
margin-top: 1.5em;
}
When I came to share my findings and thank MeltDown, I discovered that charmedbytina2 has already identified the object.

As for a link to my store, my store is not up yet. I am still learning how to customize it so that I don't expose a half-baked web site prematurely.

Thanks again!
Daniel