Although I am having trouble with level 4 menu, I have got level 5 to work.

/*/ This is the start of sub category level 4/*/

#main_menu ul.sub_menu > li > ul.sub_menu > li >ul.sub_menu {
display: none;
position: absolute;
z-index: 99999;
top:0;
left: 50px;
background: #FFFBDE;
border-radius: 8px;
padding: 15px 0;
border: 1px solid #E1B356;
box-shadow: 1px 3px 6px #444;
-webkit-box-shadow: 1px 3px 6px #444;
-moz-box-shadow: 1px 3px 6px #444;
width:180px;
list-style: none;
list-style-position: inside;
}

#main_menu ul.sub_menu > li > ul.sub_menu > li > ul.sub_menu a {
line-height: 18px;
font-size: 15px;
float: none;
font-family: 'Source Sans Pro', Arial;
padding: 0;
font-weight: normal;
text-shadow:none !important;
color: #4d4c4b;
}


#main_menu > li:hover ul.sub_menu > li:hover ul.sub_menu {
display: block;
}

/*/ This is the end of sub category level 4/*/