[css-navigation-1][editorial] Refactor <navigation-condition> definition

Author: cdoublev

css-navigation-1/Overview.bs

@@ -208,9 +208,7 @@ The syntax of the ''@navigation'' rule is:
 with <<navigation-condition>> defined as:
 
 <pre class="prod def" dfn-type="type" nohighlight>
-<dfn><<navigation-condition>></dfn> = not <<navigation-in-parens>>
-	| <<navigation-in-parens>> [ and <<navigation-in-parens>> ]*
-	| <<navigation-in-parens>> [ or <<navigation-in-parens>> ]*
+<dfn><<navigation-condition>></dfn> = <<boolean-expr[ <<navigation-test>> ]>>
 <dfn><<navigation-in-parens>></dfn> = ( <<navigation-condition>> ) | ( <<navigation-test>> ) | <<general-enclosed>>
 <dfn><<navigation-test>></dfn> = <<navigation-location-test>> | <<navigation-type-test>>