Display of compiler errors: fade-in animation is not smooth

[jruderman]

If I edit the Rust examples near https://willcrichton.net/nota/#def-sec-places so that I get a compiler error, the compiler error fades-in in a janky way, like the background is too transparent during the fade-in.

This issue happens in all browsers I tried (Firefox Beta, Chrome Dev, Safari) (all on macOS) although the timing is slightly different in each browser.