Scale frame to 100% height on mobile

Signed-off-by: Julius Härtl <jus@bitgrid.net>

css/mobile.css

@@ -10,4 +10,9 @@
 	#content {
 		padding-top: 0;
 	}
+
+	#richdocumentsframe {
+		height: 100vh;
+	}
+
 }