- main_nav_css & main_nav_js were added when the new slim sidebar was being built
- with the legacy styles/js - there was little risk of there being conflicts
- with the new sidebar CSS, this sidebar bundle comes with a large duplicate of what is in core.css so we should add it before the hooks run so that hook scan override if needed as per our documentation
- this is a temporary fix for #7943 - ideally we should avoid sidebar.scss bundle duplicating so much of the core css
- note: JS is lower risk but should follow the same convention