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

// This is needed until something like https://github.com/WordPress/gutenberg/issues/24473 exists
.site-header {
	align-items: center;
	flex-wrap: wrap;
	justify-content: space-between;
	display: flex;
	overflow: inherit;

	.wp-block-site-title a {
		text-decoration: none;
	}
}

h1, h2, h3, h4, h5, h6 {
	&.has-background {
		padding: var(--wp--custom--padding--vertical) var(--wp--custom--padding--horizontal);
	}
}