as Katie told you in the other thread https://ww.wp.xz.cn/support/topic/the-best-way-to-add-a-zotpress-like-search-on-a-page-that/#post-8874773
you can modify font size — both in general and for specific CSL elements — in CSS. The are many plugins you can use to easily implement custom CSS
Just to say we have the same issue, e.g. on https://methodscoordinationproject.org/general-introduction/ That’s with ZotPress 6.1.6 on WP 4.7.2
Happy to try to help further troubleshoot if I can be of assistance (though my understanding of WordPress is limited)
