web: Fix blue line appearing above big buttons on firefox

Signed-off-by: Eduardo L. Buratti <elb09@c3sl.ufpr.br>

web/assets/less/big-button.less

@@ -80,13 +80,13 @@
 
     .big-button:after {
         float: right;
-        height: 60px;
+        height: 61px;
         content: '';
         width: 8px;
         left: 8px;
         background-color: white;
         position: relative;
-        top: -60px;
+        top: -61px;
     }
 
     .big-button.active {