Browsers are starting to roll out changes in default UA styles for nested section headings. Developers should check that their sites don't rely on UA styles for certain cases to avoid unexpected results and failing Lighthouse checks
Default styles for h1 elements are changing | MDN Blog
Browsers are starting to roll out changes in default UA styles for nested section headings. This post describes the incoming changes, how to identify if it's an issue on your websites, and hints for conformant and better-structured pages.