[css-grid] Fix example alignment.

Author: tabatkins

css-grid/Overview.bs

@@ -1472,7 +1472,7 @@ Explicit Grid Shorthand: the 'grid-template' property</h3>
 				<pre>
 					grid-template: auto 1fr auto /
 					  (header-top) "a   a   a"     (header-bottom)
-						(main-top) "b   b   b" 1fr (main-bottom);
+					    (main-top) "b   b   b" 1fr (main-bottom);
 				</pre>
 
 					is equivalent to
@@ -1481,7 +1481,7 @@ Explicit Grid Shorthand: the 'grid-template' property</h3>
 					grid-template-columns: auto 1fr auto;
 					grid-template-rows: (header-top) auto (header-bottom main-top) 1fr (main-bottom);
 					grid-template-areas: "a a a"
-										 "b b b";
+					                     "b b b";
 				</pre>
 			</div>
 	</dl>