.MainMenu_SubMenu styles the submenu holder/container, but not the submenu items themselves.
"Item" means the actual text... they are styled by .MainMenu_MenuItem unless over-ridden.
Add one more class below yours, so the submenu items get styled:

.MainMenu_SubMenu .MainMenu_MenuItem {
background-color: #ccccff;
color: #660000;
z-index: 1000;
cursor: pointer;
cursor: hand;
}

I did, but here goes again:

Add one more class below yours, so the submenu items get styled:

.MainMenu_SubMenu .MainMenu_MenuItem {
background-color: #ccccff;
color: #660000;
z-index: 1000;
cursor: pointer;
cursor: hand;
}