Use Title: meta instead of explicit <h1>

Author: tantek

css-align-3/Overview.bs

@@ -1,6 +1,5 @@
-<h1>CSS Box Alignment Module Level 3</h1>
-
 <pre class='metadata'>
+Title: CSS Box Alignment Module Level 3
 Shortname: css-align
 Level: 3
 Group: csswg