[css-mixins-1][editorial] Tweak markup

Author: tabatkins

css-mixins-1/Overview.bs

@@ -1294,10 +1294,10 @@ Its grammar is:
 		/* Invokes --two with one argument, and no contents. */
 
 		@apply --three {color: red;}
-		/* Invokes --three with no arguments, but with contents.
+		/* Invokes --three with no arguments, but with contents. */
 
 		@apply --four(blue) {color: red;}
-		/* Invokes --four with both an argument and contents.
+		/* Invokes --four with both an argument and contents. */
 	}
 	</pre>
 </div>
@@ -1355,12 +1355,12 @@ having a <<declaration-list>> block makes the ''@apply'' rule invalid
 
 	<pre highlight=css>
 	@mixin --just-contents(@contents) {
-		@contents { content: "This is fallback." }
+		@contents { color: red; }
 	}
 
 	.foo {
 		@apply --just-contents;
-		/* substitutes with `content: "This is fallback.";` */
+		/* substitutes with `color: red;` */
 	}
 	.bar {
 		@apply --just-contents {};