Run custom CSS in WordPress admin screens

custom-admin-css.php

<?php

/**
 * Add CSS to Events Admin pages
 */

add_action('admin_head', 'my_custom_fonts');

function my_custom_fonts() {
    // Get current screen if targeting post type is necessary
    $screen = get_current_screen();
  
    if ( $screen->post_type == 'post_type' ) :
        echo '<style>
                selector {
                  property:value;
                }
            </style>';
    endif;
  
}