Change colour of navigation menu

I wish to change the menu from black to white and I have used this code to change the menu text colour and menu

#access-primary-menu li.menu-item a {
  color: black;
}
.main-navigation { 
	background-color:white; 
}
#header-menu ul.menu a
{
  padding: 0 2em;
	border-right: none;
	background-color: white;

}

but it leaves black vertical lines on the left of each menu item (except home). I cannot find where to make this white also. Can you help please?