Bug 1620130 - Fix row highlight not displaying on Ocean and default themes

Change-Id: Ic9ab99c571f9f308605c1c92a08faa81fe5a9867
behatnotneeded: styling only

htdocs/theme/raw/sass/components/_framework.scss

 .tablematrix {
     position: relative;
+    z-index: 1;
 
     tr {
         &.standard {