Has anyone used https://securityheaders.com/ to check for missing headers? Need to improve upon a D grade without breaking my sites

Hi All, One of our hosting clients recently scan their website using this server: Content-Security-Policy X-Frame-Options tells the browser whether you want to allow your site to be framed or not. By preventing a browser from framing your site you can defend against attacks like clickjacking. Recommended value "X-Frame-Options: SAMEORIGIN". X-Content-Type-Options Referrer-Policy Permissions Policy is a new header that allows a site to control which features and APIs can be used in the browser. But our sys admin's initial attempt to add these headers to Apache (via WHM tweaks, I believe) had the apparent visual effort of removing/disabling all formatting/stylesheets from all websites on the server, such that what was left was not much more than text. So now we have to go back to the drawing board, to work out how we can improve that score, without negatively impacting our hosted websites. Keen to share the experience with others. Btw we use CloudLinux OS, plus Litespeed as a drop-in replacement for Apache, in case that makes a difference. Thanks all, Ross