How to change default css?

Apparently, Perfect Survey writes its css code directly into index.php (see the mentioned page https://clausfaber.net/blog/fakten-sind-wie-kuehe/, it’s in line 313). This is annoying: css in the html code takes precedence to code in css files, and this prevents styling via the wordpress theme editor. I need to override every change with the “!important” flag, and too many of these flags make a mess and redundant code.

Is there any way to make the plugin write its code into a separate css file so that I can style it with the wordpress theme editor?

Many thanks, Claus

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