The black square that shows up on mobile devices allowing to close the menu on touchscreens can be styles with the selectors below. I recommend only changing colors/fonts.
#megaMenu ul.megaMenu li.menu-item a span.uber-close, #megaMenu ul.megaMenu li.menu-item span.um-anchoremulator span.uber-close{ top:0; right:0; background:#999; background:rgba( 0, 0, 0, .9 ); font-size:20px; font-weight:bold; color:#f5f5f5; }
Styling the open and closed states
/* Style the "x" */ #megaMenu ul.megaMenu li.menu-item a span.uber-close[data-uber-status="open"], #megaMenu ul.megaMenu li.menu-item span.um-anchoremulator span.uber-close[data-uber-status="open"]{ background:red; } /* Style the down arrow */ #megaMenu ul.megaMenu li.menu-item a span.uber-close[data-uber-status="closed"], #megaMenu ul.megaMenu li.menu-item span.um-anchoremulator span.uber-close[data-uber-status="closed"]{ background:blue; }