[css-ui-4] Clarify phrasing on when it is ok to ignore some properties

Author: frivoal

css-ui-4/Overview.bs

@@ -1886,8 +1886,8 @@ Animation type: discrete
 
 </dl>
 
-On form control elements where the computed value is ''appearance/auto''
-and on other elements where the computed value is not ''appearance/auto'', ''appearance/none'', or one of the <<compat>> values,
+On form control elements where the computed value is ''appearance/auto'' or one of the <<compat>> values,
+and on other elements where the computed value is ''appearance/button'',
 UAs may disregard some CSS properties
 to ensure that the intended appearance is preserved,
 or because these properties may not be meaningful for the chosen appearance.