Thanks for the quick response!
I applied this CSS but found two issues:
1) It is being overridden by the border style I've put in .ux-menu-item-main:
.ux-menu-item-main {
border-left-color :#ffffff;
border-left-style :solid;
border-left-width :1px;
border-right-color :#ffffff;
border-right-style :solid;
border-right-width :1px;
}
2) It's affecting the sub menu items (see attached)
Perhaps I need more (and more granular) style tags to target the appropriate menu elements. I am attaching the css file, perhaps you can take a quick looks to see where my style tags are in conflict?