Fix expression width to adjust correctly to page width

[jaltekruse]

This currently isn't great in two major ways. The maximum width never fills the page on a wide display, and the width doesn't adjust down correctly and can bleed outside of its container visually. Eventually when the widow is scaled down enough, it is too long and jumps down the page confusingly. Need to just dynamically calculate the width in javascript, I couldn't figure out how to get this to behave how I wanted it to using pure CSS.

https://user-images.githubusercontent.com/365366/162997249-55e95498-3924-43ec-8829-9509e6ecd919.mp4