prevent iframes from offsetting presentation

css/reveal.css

@@ -275,6 +275,7 @@ body {
   position: relative;
   width: 100%;
   height: 100%;
+  overflow: hidden;
   -ms-touch-action: none;
       touch-action: none; }
 

css/reveal.scss

@@ -352,6 +352,7 @@ body {
 	position: relative;
 	width: 100%;
 	height: 100%;
+	overflow: hidden;
 	touch-action: none;
 }