[css-text-decor-3] Fix spelling mistakes

Author: frivoal

css-text-decor-3/Overview.bs

@@ -205,14 +205,14 @@ Text Decoration Lines: the 'text-decoration-line' property</h3>
         Note that not blinking the text is one technique to satisfy <a href="https://www.w3.org/TR/UAAG/guidelines.html#tech-on-off-blinking-text">checkpoint 3.3 of WAI-UAAG</a>.
         This value is <strong>deprecated</strong> in favor of Animations [[CSS3-ANIMATIONS]].
     <dt><dfn value for="text-tecoration-line">spelling-error</dfn>
-      <dd>This values indicates the type of text decoration used by the User Agent
+      <dd>This value indicates the type of text decoration used by the User Agent
           to highlight spelling mistakes.
-	  It's appearance is UA defined.
+	  Its appearance is UA defined.
 	  <span class=note>It is often rendered as a red wavy underline.</span>
     <dt><dfn value for="text-decoration-line">grammar-error</dfn>
-      <dd>This values indicates the type of text decoration used by the User Agent
+      <dd>This value indicates the type of text decoration used by the User Agent
           to highlight grammar mistakes.
-	  It's appearance is UA defined.
+	  Its appearance is UA defined.
 	  <span class=note>It is often rendered as a green wavy underline.</span>
   </dl>