If, a plugin is linking to external/loading CSS, do the following.

In the plugin folder search for “wp_enqueue_style”. The first parameter is the function name.

wp_enqueue_style( 'tablepress-default'

In funtions.php add:

/**
 * Disable style sheet
 */
add_action( 'wp_print_styles', 'my_deregister_styles', 100 );
function my_deregister_styles() {
    wp_deregister_style( 'tablepress-default' );
}