style tweak

css/reveal.css

@@ -277,9 +277,10 @@ html:-moz-full-screen-ancestor {
   bottom: 8px;
   opacity: 0.5;
   z-index: 31;
+  font-family: Helvetica, sans-serif;
   font-size: 12px;
   color: #fff;
-  background-color: rgba(0, 0, 0, 0.6);
+  background-color: rgba(0, 0, 0, 0.7);
   padding: 5px; }
 
 .reveal .slide-number-delimiter {

css/reveal.scss

@@ -333,9 +333,10 @@ html:-moz-full-screen-ancestor {
 	bottom: 8px;
 	opacity: 0.5;
 	z-index: 31;
+	font-family: Helvetica, sans-serif;
 	font-size: 12px;
 	color: #fff;
-	background-color: rgba( 0, 0, 0, 0.6 );
+	background-color: rgba( 0, 0, 0, 0.7 );
 	padding: 5px;
 }