I was just looking for this struggling with my presbiopya, and after installing the extension and adding lines to settings.json ( I guessed ) with this exact contents :
"custom-ui-style.external.imports": [
".anysphere-markdown-container-root": "font-size: 14px !important; line-height: 1.5 !important;"
]
I got the warning to reload the windows by Custom UI Style
and immediately a much severe message :
“Your Cursor installations appears to be corrupt. Please Reinstall.”
Then I removed both settings and plugin and prayed 
for a few seconds, luckly it worked !
Then I went to the 2nd post found ( mentioning this one ) and found the best way to do it :
Ctrl+CMD +
GENIOUS @hiteck !!! thanks a lot
and @deanrie always helps and give the best advice, constantly this was a first time and unique event, you still rank #1 community hero for me ( and I assume many of us here ).