Drupal 8 add classes to body using URL

https://www.heididev.com/add-class-body-based-path-alias-drupal-8

Turn on twig debug.

Locate view template in use.

In my case, they were in

profiles/cms/themes/contrib/bootstrap/templates/views

In views-view.html.twig I found the div containing the views-content class.

Adding "container" to views-content and to views-header allowed a full-width content section to behave with expected margin yet have full width background image.