[css-fonts-4] Changes wrt Fonts 3, fix w3c#6882

Author: svgeesus

css-fonts-4/Overview.bs

@@ -7557,3 +7557,31 @@ Changes from the <a	href="https://www.w3.org/TR/2018/WD-css-fonts-4-20180410/">1
 	<li>Editorial cleanup, clarifying examples, markup improvements, linkfixes,
 		updating to latest references, and so on</li>
 </ul>
+
+<h3 id="changes-fonts-3">
+	Changes from the 20 September 2018
+	<a href="https://www.w3.org/TR/2018/REC-css-fonts-3-20180920/">CSS Fonts 3 Recommendation</a>
+</h3>
+
+This summarizes the changes in CSS Fonts 4, compared to CS Fonts 3.
+<!--
+	to 13 Dec 2021 see
+	https://github.com/w3c/csswg-drafts/issues/6882
+ -->
+
+<ul>
+
+    <li>Added font-display descriptor for @font-face</li>
+    <li>Added @font-feature-values rule</li>
+	<li>Added font variation properties, including font-optical-sizing and font-variation-settings</li>
+	<li>Added color font support</li>
+    <li>Defined feature-value-name for font-variant-alternates</li>
+    <li>Added new auto value for font-weight, font-style and font-stretch descriptors</li>
+    <li>Added ui-serif, ui-sans-serif, ui-monospace, and ui-rounded generic font families</li>
+    <li>Added font-size: xxx-large</li>
+    <li>Added font metric override descriptors</li>
+    <li>Added some motivation for generic font families</li>
+    <li>Added font feature technology keywords opentype, aat, and graphite</li>
+    <li>Added math value to font-size</li>
+
+</ul>