[css-values-5][editorial] Fix heading

Author: tabatkins

css-values-5/Overview.bs

@@ -339,7 +339,7 @@ Interpolated Numeric and Dimensional Values: the ''calc-mix()'' notation</h3>
 	with its arguments each computed according to their type.
 
 <h3 id="color-mix">
-Interpolated Numeric and Dimensional Values: the ''color-mix()'' notation</h3>
+Interpolated Color Values: the ''color-mix()'' notation</h3>
 
 	This specification extends the ''color-mix()'' [=functional notation=]
 	as a [=mix notation=] accepting the following syntaxes: