Hi,
Firstly, thanks for your review and feedback.
About documentation, we are correctly working whole new documentation and design that will be more helpful to users.
About your query, yes the custom CSS option is there for some advanced users who like to play with design stuffs and keep their changes while updating the theme. ??
Also, if the users request for minor tweaks we have been covering those in our free support. ?? If you have minor CSS tweak question, you can put that query in our dedicated support forum here https://themegrill.com/support-forum/forum/himalayas-free/ or you can directly mail us via this contact page https://themegrill.com/contact/ and we will provide it to you.
Thanks.