full-width delta not working

I tried making a full-width page for the Yale 2016 standard theme using the instructions found here: https://yalesites.yale.edu/book/making-page-full-width

I have created the delta and the context and confirmed that the context was working properly, but the delta doesn’t seem to be changing the page width appropriately. When I look at the page source, I don’t see the full-width class being applied anywhere, even though I added it in the content-zone>regions>content “additional region classes” field. How do I get that class active on the content wrapper?