Fix typo

Author: heycam

css-properties-values-api/Overview.bs

@@ -243,7 +243,7 @@ For example, the following are all valid syntax strings.
     and percentage values.
 :   <code>"big | bigger | BIGGER"</code>
 ::  accepts the string "big", or the string "bigger", or the string "BIGGER".
-:   <code>"&lt;length>+</code>
+:   <code>"&lt;length>+"</code>
 ::  accepts a list of length values.
 
 </div>