Forcing 3 columns on width < 640 devices. Thanks @roman01la!

Author: mrdoob

index.html

@@ -177,8 +177,8 @@
 					width: 100%;
 				}
 				#viewer img {
-					width: 100px;
-					height: 75px;
+					width: 33.33%;
+					height: auto;
 				}
 				#expandButton{
 					display: block;