Date field on Firefox

Hi,

I would like to ask you something about an appearance issue that I face with date fields of my contact form on Mozilla Firefox.

I have added the following lines at my functions.php file for making the date fields appear on firefox according to this link https://stackoverflow.com/questions/34131644/datepicker-of-cf7-not-working-in-firefox:

add_filter( 'wpcf7_support_html5_fallback', '__return_true' );
add_action('wp_head', 'replacethiswithyourthemename_wcf7_datepickerfix');
function replacethiswithyourthemename_wcf7_datepickerfix(){
    ?><style>#ui-datepicker-div {z-index:99!important;}</style><?php
}

but still the dates calendar is not appeared like it should. The date numbers are too big and they aregoing out of the box.

Could you maybe help me resolve this issue?

The page I need help with: [log in to see the link]