jump to slide tweak

css/reveal.scss

@@ -1818,7 +1818,7 @@ $notesWidthPercent: 25%;
 }
 .reveal .jump-to-slide-input::placeholder {
 	color: currentColor;
-	opacity: 0.3;
+	opacity: 0.5;
 }
 
 .reveal.has-dark-background .jump-to-slide-input {