How to disable the new WordPress block style CSS in 3 lines

If you don’t use the new WordPress blocks, you should avoid to load the block style CSS on your page to optimize the page load speed. Here the three lines you need:

add_action('wp_print_styles', function () {
  wp_dequeue_style('wp-block-library');
}, 100);

Adding the action with priority 100, it will be executed after the style has been enqueued by WordPress.

You can add this code in your functions.php theme file.