My school did not use CSS for financial aid but you should reach out to the financial aid office for clarification. In my experience, my school asked the reason I could not complete parental data on FAFSA and the institutional aid applications. They told me I could be considered for federal loans without it, but it was required for institutional aid (needs-based loans with reduced interest and/or scholarships). Then, after a long and detailed appeals process where I had to obtain third party documentation on parental estrangement, I was allowed to be considered for institutional aid. The whole financial aid process is definitely overwhelming at times and I hope you're able to get an answer!
