[css-scroll-snap-1] Use html instead of body: scroll snap doesn't propagate from body.

Author: fantasai

css-scroll-snap-1/Overview.bs

@@ -494,7 +494,7 @@ Scroll Snapport: the 'scroll-padding' property {#scroll-padding}
         that is not obscured by a fixed-position toolbar.
 
         <pre class="lang-css">
-            body {
+            html {
                 overflow-x: auto;
                 overflow-y: hidden;
                 scroll-snap-type: x mandatory;