[css-regions-1] Add whitespaces around combinator (#9132)

Author: cdoublev

css-regions-1/Overview.bs

@@ -381,7 +381,7 @@ The 'flow-into' property</h3>
 
 	<pre class='propdef'>
 		Name: flow-into
-		Value: none | <<ident>> [element|content]?
+		Value: none | <<ident>> [element | content]?
 		Initial: none
 		Applies To: All elements, but not <a href="https://www.w3.org/TR/selectors/#pseudo-elements">pseudo-elements</a> such as <code>::first-line</code>, <code>::first-letter</code>, <code>::before</code> or <code>::after</code>.
 		Inherited: no