Align static modals with accessibility panel markup

components/bug-fix-form.html

@@ -14,7 +14,7 @@
 >
   <div class="bv-modal-backdrop" data-dismiss></div>
 
-  <div class="modal-sheet">
+  <div class="bv-modal__panel modal-sheet" tabindex="-1">
     <!-- Header bar (sticky) with updated title styling -->
     <div class="modal-header">
       <h2