I am trying to use the Drupal 8 Modal API to output a link in a modal window - using the "Simple Link" approach here.
When clicking my link, I get a little animated spinner and I can see the response being returned via ajax using my browser inspector. However, no modal appears? There are no errors output to the console.
I am using a custom theme - is there some mark up I must place in the theme, to act as a container for the modal?