Admonition stretches to width of page

As you can see in this screenshot, the admonition named ‘Abstract’ stretches to the whole of the page, ever since the latest minimal theme update.

Things I have tried

I tried searching for admonition width but didn’t find anything.

What I’m trying to do

I’d like it to be the width of the rest of the text, as it used to be.
Thanks in advance for any help.