ui-icon-triangle-1-s missing

ui-icon-triangle-1-s missing

I am using jquery.ui.combify to display combo boxes.
In a test programme the south-pointing arrow is displayed as normal but when integrated into the live programme the arrow is missing even though the functionality works.
I am guessing that I have a missing library or an old library.
Any advice is appreciated.
Thanks

My header information is as follows:

  1.     <script src="includes/jquery-3.2.1.min.js"></script>
        <script language='JavaScript1.1' src='scripts/ap-base.js'></script>

        <script src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.10.4/jquery-ui.min.js"></script>
        <script type="text/javascript" src="includes/jquery.ui.combify.js"></script>
        <link rel="stylesheet" href="https://ajax.googleapis.com/ajax/libs/jqueryui/1.10.4/themes/smoothness/jquery-ui.css" type="text/css" media="all" />