[css-values-4][meta] Fix linking error.

Author: tabatkins

css-values-4/Overview.bs

@@ -2247,7 +2247,7 @@ Toggling Between Values: ''toggle()''</h3>
 	not a particular serialization [[!CSS21]],
 	so comparison between computed values should always be unambiguous and have the expected result.
 	For example,
-	a Level 2 <a property spec=css21>background-position</a> computed value
+	a Level 2 <l spec=css2>'background-position'</l> computed value
 	is just two offsets, each represented as an absolute length or a percentage,
 	so the declarations ''background-position: top center'' and ''background-position: 50% 0%''
 	produce identical computed values.