Import bootstrap 5 and bootstrap icons in wp-admin backend
Basically, to add admin-style.css to admin: function wpdocs_enqueue_custom_admin_style() { wp_register_style( ‘custom_wp_admin_css’, get_template_directory_uri() . ‘/admin-style.css’, false, ‘1.0.0’ ); wp_enqueue_style( ‘custom_wp_admin_css’ ); } add_action( ‘admin_enqueue_scripts’, ‘wpdocs_enqueue_custom_admin_style’ ); Do approximately the same for Javascript. See https://developer.wordpress.org/reference/hooks/admin_enqueue_scripts/ And see https://wordpress.stackexchange.com/search?q=custom+css+admin