Changing the sub menu colors.

Hi everyone, I have bee trying to customize the colors of the menu and submenus. I was able to change the menu through stylesheet using this:

.dropdown-menu li {
border-top: 1px solid #31363A;
border-bottom: 1px solid #000;
}

However, when trying to change the submenu items, the stylesheet seems to be ignored. tried with this:

.sub-menu .dropdown-menu .menu-item li {
background: #FFFFFF;
}

These last lines make the sub-menu item flash white (#FFFFFF) when it drops down, but instantly turns to a dark blue color. Seems like there is something else overriding and applying some kind off fade-in effect when the mouse is over.

Any ideas on how to change this settings?

Thanks!