[css-contain] Fix indentation

Author: frivoal

css-contain-1/Overview.bs

@@ -282,7 +282,7 @@ Style Containment</h3>
 	<pre><code highlight=css>
 	div {
 		contain: style;
-		 counter-increment: n;
+		counter-increment: n;
 	}
 	div::before {
 		counter-increment: n 2;