[css-values-4] Partially-simplify min/max(), per w3c#4756.

Author: tabatkins

css-values-4/Overview.bs

@@ -4072,6 +4072,24 @@ Simplification</h4>
 				expressed in the result's [=canonical unit=].
 
 			5. Return |root|.
+
+		8. If |root| is a Min or Max node:
+
+			1. [=For each=] node |child| of |root|’s children:
+
+				If |child| is a numeric value
+				with a unit other than "percent",
+				and there are other children of |root|
+				that are numeric values with the same unit,
+				combine all such children
+				with the appropriate operator per |root|,
+				and replace |child| with the result,
+				removing all other child nodes involved.
+
+			2. If |root| now has only a single child,
+				return that child.
+				Otherwise, return |root|.
+
 	</div>
 
 <h3 id='calc-computed-value'>