Custom menu not support dropdown menu.
Here is rough style rules.
Impact to the display of other widgets are not taken into account.
.rsidebar,
.lsidebar{
overflow:visible;
}
.rsidebar .children,
.rsidebar .sub-menu,
.lsidebar .children,
.lsidebar .sub-menu{
display:none;
}
.rsidebar li,
.lsidebar li{
position:relative;
}
.rsidebar a,
.lsidebar a{
display:block;
width:100%;
height:100%;
}
.yui-t3 .lsidebar .children:hover,
.yui-t3 .lsidebar .sub-menu:hover,
.yui-t3 .lsidebar a:hover + .children,
.yui-t3 .lsidebar a:hover + .sub-menu,
.yui-t2 .lsidebar .children:hover,
.yui-t2 .lsidebar .sub-menu:hover,
.yui-t2 .lsidebar a:hover + .children,
.yui-t2 .lsidebar a:hover + .sub-menu,
.yui-t1 .lsidebar .children:hover,
.yui-t1 .lsidebar .sub-menu:hover,
.yui-t1 .lsidebar a:hover + .children,
.yui-t1 .lsidebar a:hover + .sub-menu{
display:block;
position:absolute;
left:100%;
top:-.4em;
width:12em;
background:#333;
}
.lsidebar .children:hover,
.lsidebar .sub-menu:hover,
.yui-t6 .lsidebar .children:hover,
.yui-t6 .lsidebar .sub-menu:hover,
.yui-t6 .lsidebar a:hover + .children,
.yui-t6 .lsidebar a:hover + .sub-menu,
.yui-t5 .lsidebar .children:hover,
.yui-t5 .lsidebar .sub-menu:hover,
.yui-t5 .lsidebar a:hover + .children,
.yui-t5 .lsidebar a:hover + .sub-menu,
.yui-t4 .lsidebar .children:hover,
.yui-t4 .lsidebar .sub-menu:hover,
.yui-t4 .lsidebar a:hover + .children,
.yui-t4 .lsidebar a:hover + .sub-menu,
.rsidebar .children:hover,
.rsidebar .sub-menu:hover,
.rsidebar a:hover + .children,
.rsidebar a:hover + .sub-menu{
display:block;
position:absolute;
left:-11.5em;
top:-.4em;
width:12em;
background:#333;
}
Thank you.