[css-writing-modes] Fix typo

Author: kojiishi

css-writing-modes/Overview.bs

@@ -1653,10 +1653,10 @@ Line-relative Directions</h3>
     When ''text-orientation: upright'',
     the baseline is still vertical,
     and the vertical baseline in the font is used,
-    or vertical baseline is synthesized if the font does not provide.
+    or the vertical baseline is synthesized if the font does not provide.
   <p>
     Since the baseline is vertical,
-    the definitions for ''sideways-right'' still applies; i.e.,
+    the definitions for ''mixed'' or ''sideways-right'' above still applies; i.e.,
     <a>line-over</a> is on right, and <a>line-under</a> is on left.
   </div>