Code blocks won't shrink

[elstoc]

I'm trying to incorporate react-markdown into my project and I can't seem to persuade my code blocks to shrink and include scroll bars when my page width shrinks. Whatever I do, the code block will only shrink as far as the longest line within it.

When I look at the generated html it looks like all the code is contained in quotation marks within the tag and when I select the text within those quotation marks the browser doesn't seem to like it -- it says "no matching selector or style". Is there any way around this, or is it intrinsic to how the blocks are rendered?

For example:

[elstoc]

Never mind. It seems it was a behaviour I introduced somehow, because an older version of my app works fine.