Use display rather than visibility to remove closed expansion panel content from the flow.

Author: josephperrott

src/lib/expansion/expansion-panel.ts

@@ -81,8 +81,8 @@ export type MatExpansionPanelState = 'expanded' | 'collapsed';
   ],
   animations: [
     trigger('bodyExpansion', [
-      state('collapsed', style({height: '0px', visibility: 'hidden'})),
-      state('expanded', style({height: '*', visibility: 'visible'})),
+      state('collapsed', style({height: '0px', display: 'none'})),
+      state('expanded', style({height: '*', display: 'block'})),
       transition('expanded <=> collapsed', animate(EXPANSION_PANEL_ANIMATION_TIMING)),
     ]),
   ],