Hello,
please try this css:
.unit_prevnext a.unit.unit_button>span:after {
content: "\e172" !important;
font-family: 'fonticon';
float: left;
margin-right: 5px;
margin-top: 1px;
}
#prev_unit:after, #prev_quiz:after {
content: "\e172";
font-family: 'fonticon';
float: left;
margin-right: 5px;
margin-top: 1px;
}
some how your unit id is missing that is why it is not applying.
refer:
http://prntscr.com/oz4qh9
this could be anything. obsolete version of plugins, 3rd party conflict, external custom codes anything.