fix concave/convex transitions on vertical slides #1947

css/reveal.css

@@ -486,7 +486,8 @@ body {
           perspective-origin: 50% 40%; }
 
 .reveal .slides > section {
-  -ms-perspective: 600px; }
+  -webkit-perspective: 600px;
+          perspective: 600px; }
 
 .reveal .slides > section,
 .reveal .slides > section > section {

css/reveal.scss

@@ -588,7 +588,7 @@ $controlsArrowAngleActive: 36deg;
 }
 
 .reveal .slides>section {
-	-ms-perspective: 600px;
+	perspective: 600px;
 }
 
 .reveal .slides>section,