I modified the CCS as below, but it only increased “Menu” Width, not of “Sub Menu” Width.
}
.main-navigation ul ul {
box-shadow: 0 3px 3px rgba(0, 0, 0, 0.2);
display: none;
float: left;
position: absolute;
top: 1.5em;
left: 0;
z-index: 99999;
width:250px;
text-align:left;
}