Custom menu styling

I think you can use the text-indent for this level, but you must set the text-indent for all a -tags of the class sub-menu also set to 0, not -999px.

Example:

#menu-main-navigation .link-experience a {
display: block;
height: 63px;
width: 167px;
text-indent: -999px;
}

.sub-menu a {
text-indent: 0px !important;
}