[MJ]

Ah, I understand, thank you. I have added bootstrap loading to the Child Theme – Theme Functions (functions.php) file, all good now.

For the benefit of others:

add_action( 'wp_enqueue_scripts', 'theme_enqueue_styles' );
function theme_enqueue_styles() {
 
    $parent_style = 'parent-style';
    wp_enqueue_style( 'bootstrap-style', get_template_directory_uri().'/assets/library/bootstrap/css/bootstrap.min.css', array(), '4.0.0');
    wp_enqueue_style( $parent_style, get_template_directory_uri() . '/style.css' );
    wp_enqueue_style( 'child-style',
        get_stylesheet_directory_uri() . '/style.css',
        array( $parent_style ),
        wp_get_theme()->get('Version')
    );
}