Boostrap 4 migration, hidden-* classes in the boost theme

Test footer flat menu visibility: Login as admin. Navigate to Site administration > Appearance > Theme Settings. Copy the custom menu example for form field "Custom menu items" into the form field text area. Navigate home. Verify custom menu items are visible. Reduce / increase the browser size. Verify the custom menu items disappear from the navbar on smaller browser sizes. When hidden in navbar the menu items should be visible in the site footer. Test hidden print  Login as any user, it does not matter what role you have. Navigate to any page that has a block area, often courses have a block area. Print preview the page (don't waste any paper!) The block area contents should not be visible on print.