Change jagged misspelled word underline to be smooth

Things I have tried

I tried looking into the CSS mentioned here: Custom css for spellcheck - #2 by Silver, but I don’t see anything that would be obviously useful in my use case.

What I’m trying to do

I am trying to change the misspelled word underline to something less harsh and jagged like a simple smooth red underline. I know this is very minor, but I often want to keep an unrecognized word as misspelled and continue to be reminded, and also don’t want to add it to the dictionary. In the meantime, while in this state, I’d like to keep spellcheck on but not be so distracted by the red jagged line. Instead, I would like to have a smooth underline. Thanks for any suggestions.