Sometimes you need to remove the datepicker default CSS style that comes with Toolset, for instance, when you are using a theme that has some datepicker styles already.
For your info, this file is in the common library and it’s present in several Toolset plugins.

add_action('wp_enqueue_scripts', 'remove_datepicker_styles', 100);
function remove_datepicker_styles(){
    wp_dequeue_style('wptoolset-field-datepicker');
}