fix alpha overlap during scrolled code highlight transitions

css/reveal.scss

@@ -1636,6 +1636,10 @@ $overlayHeaderPadding: 5px;
 	opacity: 0.4;
 }
 
+.reveal .hljs.has-highlights.fragment {
+	transition: all .2s ease;
+}
+
 .reveal .hljs:not(:first-child).fragment {
 	position: absolute;
 	top: 0;

plugin/highlight/plugin.js

@@ -194,6 +194,8 @@ const Plugin = {
 		var startTop = block.scrollTop;
 		var targetTop = highlightBounds.top + ( Math.min( highlightBounds.bottom - highlightBounds.top, viewportHeight ) - viewportHeight ) / 2;
 
+		console.log(startTop, targetTop)
+
 		// Account for offsets in position applied to the
 		// <table> that holds our lines of code
 		var lineTable = block.querySelector( '.hljs-ln' );