themes-wordpress/strand/parts/header.html

<!-- wp:group {"style":{"position":{"type":"sticky","top":"0px"}},"layout":{"type":"constrained"}} -->
<div class="wp-block-group"><!-- wp:site-title /-->

<!-- wp:site-tagline /-->

<!-- wp:jetpack/subscriptions {"buttonOnNewLine":true,"buttonWidth":"100%","buttonBackgroundColor":"background","textColor":"primary","borderColor":"background"} /--></div>
<!-- /wp:group -->