[css-forms-1] Add 'approximate' wrt order of principles

Author: fantasai

css-forms-1/Overview.bs

@@ -57,7 +57,7 @@ spec:css-forms-1; type:value; for:/; text:::placeholder
 ## Design Principles for the [=Basic Appearance=] ## {#basic-appearance-principles}
 
   The following design principles apply to the design of the [=basic appearance=] stylesheet for form controls,
-  in order of descending importance:
+  in approximate order of descending importance:
 
   1. The styles are identical in every user agent.
   1. The controls are recognizable and usable on their own without additional styles.