[css-pseudo] non-substantive prose tweaks

Author: delan

css-pseudo-4/Overview.bs

@@ -789,7 +789,7 @@ Cascading and Per-Element Highlight Styles</h3>
   When multiple styles conflict,
   the winning style is determined by the cascade.
   When any supported property is not given a value by the cascade,
-  it's value is determined by inheritance from
+  its value is determined by inheritance from
   the corresponding <a>highlight pseudo-element</a>
   of its <a>originating element</a>'s parent element
   (regardless of whether that property is an <a>inherited property</a>).
@@ -1000,7 +1000,7 @@ Security and Privacy Considerations</h3>
 
   Because the styling of spelling and grammar errors
   can leak information about the contents of a user's dictionary
-  (which can include the user's name and even includes the contents of his/her address book!)
+  (which can include the user's name and even includes the contents of their address book!)
   UAs that implement ''::spelling-error'' and ''::grammar-error''
   must prevent pages from being able to read
   the styling of such highlighted segments.