Add the following code snippet in your theme style.css
/* bbpress specific styling */ #bbpress-forums, #bbpress-forums ul.bbp-forums, #bbpress-forums ul.bbp-lead-topic, #bbpress-forums ul.bbp-replies, #bbpress-forums ul.bbp-search-results, #bbpress-forums ul.bbp-topics, div.bbp-template-notice li, div.bbp-template-notice p, div.bbp-breadcrumb, div.bbp-topic-tags { font-size: .9rem; line-height: 1.5; } #bbpress-forums .bbp-forum-info .bbp-forum-content, #bbpress-forums p.bbp-topic-meta, span.bbp-admin-links a { font-size: .9rem; }