Hi there!

Thanks for your request.

Actually here is all you need to know about custom code related to our Helix Ultimate framework:

https://www.joomshaper.com/documentation/helix-framework/helix-ultimate-2/custom-code-css-js-meta

And the following blog post may help you to identify which portion of code you need to modify with the help of the browser inspector:

https://www.joomshaper.com/blog/which-line-of-css-i-have-to-edit-code-inspector-in-action

However, actually you will get many lessons online to learn CSS. For example: https://www.w3schools.com/css/default.asp

But there is no documentation about it because we do not teach CSS here. You will find some most useful tips within specific product documentations.

Hope this helps!

Best Regards