Update Overview.bs (#9613)

Fixing a typo

Author: kizu

css-anchor-position-1/Overview.bs

@@ -460,7 +460,7 @@ and/or the "end region" between the last two.
 		Like in ''anchor()'',
 		the plain logical keywords
 		(''inset-area/start'', ''inset-area/end'', etc)
-		refer to the writing mdoe of the element's [=containing block=].
+		refer to the writing mode of the element's [=containing block=].
 		The ''inset-area/x-start''/etc determine their direction in the same way,
 		but in the specified physical axis.