[css-scrollbars-1] Fix some internal linking.

Author: upsuper

css-scrollbars-1/Overview.bs

@@ -139,10 +139,10 @@ Percentages: n/a
 This property allows the author to set the maximum thickness of an element’s scrollbars when they are shown.
 
 <dl dfn-type="value" dfn-for=scrollbar-width>
-<dt><dfn >''auto''</dfn></dt>
+<dt><dfn>auto</dfn></dt>
 <dd>implementations must use the default platform scrollbar width.
 </dd>
-<dt><dfn for=scrollbar-width>''thin''</dfn></dt>
+<dt><dfn>thin</dfn></dt>
 <dd>implementations must use either a thin scrollbar width variant on platforms that provide that option, 
 or display a scrollbar thinner than the default platform scrollbar width.
 </dd>