Possible to create a max height for a code block?

I'm having the same problem as this person, where side-by-side code blocks overlap https://answers.squarespace.com/questions/229853/code-block-image-overlapping.html

So instead of keeping the mailchimp emails side by side, I'd like to stack them — but in order to do that without the page being way too ridiculously long, I'd like to cut each block off at a certain height, wherein a visitor can scroll within the block to read the full email, or scroll outside it to go lower down on the page. This must be possible...somehow...right?

Side note, this is a really annoying issue! Why are code blocks not dynamic!?