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Default styles for h1 elements are changing


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.

In general, this created confusion about where developers could use<h1> elements, tools handled the HTML differently, and the outline algorithm was considered problematic. Alongside the changes in browser styles, page auditing tools like Lighthouse now flag cases of<h1> s without defined font-size as bad practice. From March 31, 2025, Firefox is rolling out changes to 50% of Beta 138 users to remove UA styles for h1 in article, aside, nav, or section on desktop.

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Photo of H1 elements

H1 elements

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Default styles