Thanks Mariya, your suggestion helped. However I had to tune it as follows:
/*applied to the menu's li elements.*/.jqx-menu li, .jqx-menu-dropdown li{ line-height: 1.3 !important; -moz-border-radius: 0px; -webkit-border-radius: 0px; border-radius: 0px;}/*applied to the menu's li elements.*/.jqx-menu li{ border-right: 1px solid black;}
But now the last menu item has a “separator” on the right. I will try to use some JavaScript to remove it.