[css-shadow-parts-1][editorial] Fix link syntax.

Author: tabatkins

css-shadow-parts-1/Overview.bs

@@ -442,8 +442,8 @@ The rules for parsing a list of part mappings are as follow:
 
 1. Let <var>input</var> be the string being parsed.
 
-1. <span data-x="split a string on commas">Split the string <var>input</var> on
-    commas</span>. Let <var>unparsed mappings</var> be the resulting list of strings.
+1. [=split a string on commas|Split the string <var>input</var> on commas=].
+    Let <var>unparsed mappings</var> be the resulting list of strings.
 
 1. Let <var>mappings</var> be an initially empty [=list=] of [=pairs=] of tokens.
     This [=list=] will be the result of this algorithm.