[css-ui-4][editorial] Added Changes from L3 section

Added a rough overview of new and changed features since CSS UI 3.

Author: SebastianZ

css-ui-4/Overview.bs

@@ -4309,6 +4309,52 @@ Changes from the <a href="https://www.w3.org/TR/2015/WD-css-ui-4-20150922/">22 S
 			Content from the now-stable [[CSS-UI-3]] has been merged in.
 	</ul>
 
+<h3 id="changes-L3" class=no-num>
+Changes from <a href="https://www.w3.org/TR/css-ui-3/">CSS UI Level 3</a></h3>
+
+	<ul>
+		<li>
+			Added the directional focus navigation properties 'nav-up', 'nav-down', 'nav-left', and 'nav-right'.
+
+		<li>
+			Added the 'appearance' property.
+
+		<li>
+			Moved ''resize: block'' and ''resize: inline'' from [[CSS-LOGICAL-1]] to this specification.
+
+		<li>
+			Added the 'accent-color' property.
+
+		<li>
+			Added the 'interest-delay' property and its longhands 'interest-delay-start' and 'interest-delay-end'.
+
+		<li>
+			Added the 'pointer-events' property.
+
+		<li>
+			Extended the image types required to be supported for the 'cursor' property
+			from just <<url>> to <<url>> and <<url-set>>.
+			(Support for the broader <<image>> type remains allowed but optional.)
+
+		<li>
+			Retired the <code>invert</code> value of 'outline-color'.
+
+		<li>
+			Added the ''outline-color/auto'' value of 'outline-color'.
+
+		<li>
+			Added the 'caret-animation' property.
+
+		<li>
+			Added the 'interactivity' property.
+
+		<li>
+			Added the 'interest-delay' property and its longhands 'interest-delay-start' and 'interest-delay-end'.
+
+		<li>
+			Let 'outline-color' refer to <<'border-top-color'>>, so additions to that property's values also apply to it.
+	</ul>
+
 <h2 class="no-num" id="privacy">
 Appendix C: Privacy Considerations</h2>