Following the instructions in your documentation (https://learn.getgrav.org/17/themes/customization) I created public_html/user/themes/quark/css/custom.css
Did not work at all even though custom.css appears in the source code, and yes I tried clearing cache.
After spending almost an hour trying to get it to work I found that a custom css plugin exists, which actually does work.
Could someone please enlighten me why it wasn't working without the plugin?
Cheers.