Just that im unsure if its required to learn things like sass which is more advanced.
Yeah, I would worry more about CSS than SASS, if you want to be a backend guy.
With priority of 70 percent backend and 30 percent front end.
That sounds like a good goal. Once you have a basic understanding of frontend, I might even roll that back a little more. And once you get up to and intermediate level on CSS, then maybe you can start learning SASS, etc., which will be much easier than learning CSS was.
I do a lot a job hunting, and I don’t see nearly as many jobs for “pure” backend work. Most expect you to know a little frontend. YMMV. Just keep learning. You’ll start searching the job market and get an idea what people want. There’s not perfect stack or perfect ratio of FE/BE that will automatically get you a job. Maybe start looking on job sites and see what the kind of jobs you like are looking for. If you have a job/company you really, really like, maybe even send the company an email, “Hey, I like what you do and would love to be a BE coder for you one day, on what technologies would you recommend that I work?”
Just keep learning. Pick a stack you like and learn it well. Then start branching out and familiarizing yourself with others and other supporting technologies. Eventually your growing skills, the job market, and a little luck will intersect and you’ll get the job.