[css-snappoints] Typo margin box -> border box

Author: ChumpChief

css-snappoints/Overview.bs

@@ -186,7 +186,7 @@ Overview {#overview}
 
     <a>Snap positions</a> can be specified
     as a particular alignment ('scroll-snap-align')
-    of an element's <a>scroll snap margin</a> ('scroll-snap-margin', defaulting to its margin box)
+    of an element's <a>scroll snap margin</a> ('scroll-snap-margin', defaulting to its border box)
     within the <a>scroll container</a>’s <a>snap alignment container</a>
     (the rectangle obtained by reducing its visual viewport by its 'scroll-snap-padding').
     This is conceptually equivalent to specifying the alignment of