impossible to fully customize the CSS of this plugin

Hi RUSSEL86,

you may change the style sheet specific to the plugin. Add the style sheet content to custom CSS area and change as per your requirement. primary-menu_264 class is specific to my site, it will be different in your project.

.wr-megamenu-container.primary-menu_264 {
	background: #ffffff !important;
}
.primary-menu_264 .wr-mega-menu > li:hover > a,
.primary-menu_264 .wr-mega-menu > li.focus > a {
	background: #cccccc !important;
}
.primary-menu_264 .wr-mega-menu > li > a {
	color: #000000 !important;
	font-family: Open Sans !important;
	font-size:16px !important;
	font-weight:normal !important;
}
.primary-menu_264 .wr-mega-menu > li > a > i {
	font-size: 16px !important;
}
.primary-menu_264 .wr-mega-menu a.caption {
	color: #eb1d0e !important;
	font-family: Open Sans !important;
	font-size:15px !important;
	font-weight:bold !important;
}
.primary-menu_264 ul.sub-menu li a,
ul.submenu-items li a {
	color: #b5b0b5 !important;
	font-family: Open Sans !important;
	font-size:13px !important;
	font-weight:bold !important;
}