[css-contain] Editorial tweaks

Author: frivoal

css-contain-1/Overview.bs

@@ -270,7 +270,7 @@ Layout Containment</h3>
 <h3 id='containment-style'>
 Style Containment</h3>
 
-	Giving an element <dfn export>style containment</dfn> has the following effect:
+	Giving an element <dfn export>style containment</dfn> has the following effects:
 
 	1. The 'counter-increment' and 'counter-set' properties
 	    must be <a for=property>scoped</a> to the element's sub-tree
@@ -314,7 +314,7 @@ Style Containment</h3>
 	<pre><code highlight=css>
 	div {
 		contain: style;
-		 counter-increment: n;
+		counter-increment: n;
 	}
 	div::before, div::after {
 		content: counters(n, '.') " ";