themes-wordpress/blockbase/templates/404.html

<!-- wp:template-part {"slug":"header","tagName":"header"} /-->

<!-- wp:group {"tagName":"main","layout":{"inherit":true}} -->
<main class="wp-block-group">
	<!-- wp:pattern {"slug":"blockbase/404"} /-->
	<!-- wp:search {"label":""} /-->
</main>
<!-- /wp:group -->

<!-- wp:template-part {"slug":"footer","tagName":"footer","className":"site-footer-container"} /-->