.stt-top { /* One of these will hide it without using display:none =P */
   display:block;
   text-indent:-9999em;
   font-size:0;
   line-height:0;
   height:0;
   visibility:hidden;
}
.stt-gototop {
   position:fixed;
   z-index:5000;
   bottom:80px;
   right:0px;
   background:url("https://www.s-kasahara.co.jp/koken/wp/wp-content/stt-images/totop.png") no-repeat top left;
   text-indent:-9999em;
   width:54px;
   height:54px;
   }
.stt-gototop:hover,
.stt-gototop:active,
.stt-gototop:focus {
   outline:0;
}