remove gradient from styling

bigbluebutton-html5/imports/ui/components/app/styles.scss

@@ -75,12 +75,10 @@
 
   &:before {
     top: 0;
-    background: linear-gradient(to bottom, rgba(0, 0, 0, .45) -20%, transparent 20%);
   }
 
   &:after {
     bottom: 0;
-    background: linear-gradient(to top, rgba(0, 0, 0, .45) -20%, transparent 20%);
   }
 
   @include mq($medium-up) {