It looks like the issue is caused by the css code block:
ul#cssmw ul {
cursor: default;
font-size: 0;
list-style-type: none;
margin: 0 0 0 0;
padding: 0 0 0 0;
}
The font-size is being set to 0, so when the submenu font-size is set to em, no matter how large the number of ems, the size in px will still be 0. If you remove the font-size: 0; from that, you can set the units to be em for the submenus as well as the top level menu and it will work.