Speed Optimization

We are currently using wordpress with woodmart and wpbakery page builder. When we initiate a speed test from pagespeed it gives these errors: Reduce unused CSS, Eliminate render-blocking resources, Avoid an excessive DOM size . We are additionally using LiteSpeed and cdn and tried nearly every possible setting. For example when I inspect which file is causing the error Eliminate render-blocking resources it shows css code of wpbakery. I would like to understand if these problem caused by theme and how to solve it. Thanks in advance.