'no notes on this slide' placeholder

css/reveal.css

@@ -1483,6 +1483,11 @@ body {
   text-align: left;
   font-family: Helvetica, sans-serif;
   -webkit-overflow-scrolling: touch; }
+  .reveal .speaker-notes .notes-placeholder {
+    color: #ccc;
+    font-style: italic; }
+  .reveal .speaker-notes:focus {
+    outline: none; }
   .reveal .speaker-notes:before {
     content: 'Speaker notes';
     display: block;

css/reveal.scss

@@ -1612,6 +1612,15 @@ $controlsArrowAngleActive: 36deg;
 	font-family: Helvetica, sans-serif;
 	-webkit-overflow-scrolling: touch;
 
+	.notes-placeholder {
+		color: #ccc;
+		font-style: italic;
+	}
+
+	&:focus {
+		outline: none;
+	}
+
 	&:before {
 		content: 'Speaker notes';
 		display: block;
@@ -1620,6 +1629,7 @@ $controlsArrowAngleActive: 36deg;
 	}
 }
 
+
 .reveal.show-notes {
 	max-width: 75vw;
 	overflow: visible;

js/reveal.js

@@ -2788,7 +2788,7 @@
 
 		if( config.showNotes && dom.speakerNotes && currentSlide && !isPrintingPDF() ) {
 
-			dom.speakerNotes.innerHTML = getSlideNotes() || '';
+			dom.speakerNotes.innerHTML = getSlideNotes() || '<span class="notes-placeholder">No notes on this slide.</span>';
 
 		}