Add max width to Gutenberg Editor

functions.php

add_action( 'admin_head', function () {
	global $pagenow;
	if ( ! in_array( $pagenow, array( 'post.php', 'post-new.php' ) ) ) {
		return;
	}
	?>
	<style>
		.edit-post-visual-editor .wp-block.editor-post-title,
		.edit-post-visual-editor .wp-block {
			max-width: calc(100% - 100px);
			margin-left: auto;
			margin-right: auto;
		}		
		.wp-block.block-editor-block-list__block {
			padding: 0;
		}
	</style>
	<?php
} );