'Back' and 'Next' buttons are blank?

Hi guys,
Again a question; it seems that the 'back' and 'next' buttons are 'blank'.
Any idea what it could be?
https://www.bes-it.nl/zorgsaam

They are not blank they are using white color, you can add this to custom.css to override color

.pagenav li > a {
color:#c00;
}

You can change with any color you wish.

Thank you very much! It worked (afcourse 😉 )