themes-wordpress/blockbase/sass/base/_header.scss

.wp-site-blocks .site-header {

	// Needed until Gutenberg offers responsive design options
	// TODO: Ref to responsive design options issue
	@include break-small-only(){
		.site-brand {
			display: contents;
		}
		.wp-block-site-logo {
			flex-basis: 100%;
			margin-bottom: calc( 2 * var(--wp--custom--gap--vertical));
			margin-top: var(--wp--custom--gap--vertical);
			text-align: center;
		}
	}
	
}

// Needed until Gutenberg offers responsive design options
// Used by 'header-linear' template part
.wp-site-blocks .site-header-linear {
	@include break-small-only(){
		.site-words-stack-small {
			display:block;
		}
	}
}