nav > ul > li > a {
    position:relative;
}

nav> ul> li> a:hover::after{
    content:'';
    position:absolute;
    width: 100%;
    height: 0;    
    left:0;
    bottom:-2px;
/*    border-bottom: 2px solid #FEFEFE;  */
    border-bottom: 2px solid #FF0000;  
}

.selected_menu_item a {
    bottom:0px;
/*    border-bottom: 2px solid #FEFEFE;  */
    border-bottom: 2px solid #FF0000;  
}