Update focus-returns-trigger-9au0ou.md

Author: HelenBurge

_rules/focus-returns-trigger-9au0ou.md

@@ -32,16 +32,16 @@ This rule applies to any element with a semantic role of dialog or alertdialog t
 
 The element that has the focus when the target element becomes visible is the same element that receives focus when the target element stops being visible.
 
-## Assumptions
+## Background
+
+### Assumptions
 
 There are no assumptions.
 
-## Accessibility Support
+### Accessibility Support
 
 There are no accessibility support issues known.
 
-## Background
-
 ### Bibliography
 
 - [Understanding Success Criterion 2.4.3: Focus Order](https://www.w3.org/WAI/WCAG22/Understanding/focus-order.html)