[css-color-5] order of operations, see w3c#6047

Author: svgeesus

css-color-5/Overview.bs

@@ -133,9 +133,9 @@ Mixing colors: the ''color-mix()'' function {#color-mix}
 	5. Otherwise, if both are provided but do not add up to 100%,
 	they are scaled accordingly so that they add up to 100%.
 	This means that
-	<var>p1</var> becomes <var>p1</var> / <var>p1</var> + <var>p2</var>
+	<var>p1</var> becomes <var>p1</var> / (<var>p1</var> + <var>p2</var>)
 	and
-	<var>p2</var> becomes <var>p2</var> / <var>p1</var> + <var>p2</var>.
+	<var>p2</var> becomes <var>p2</var> / (<var>p1</var> + <var>p2</var>).
 
 Issue: Should we handle p1 + p2 &lt; 100% differently? E.g. a mix with `transparent`?