Hello,
I bought “Materialize – Material Design Based Multipurpose HTML Template” very recently but I’m quite annoyed because the checkboxes don’t display with your theme.

You don’t have a sample page with all possible form fields, nothing in your documentation either, so I went to see the Materialize documentation. And their code doesn’t work either.
I finally found something that works in a bootstrap documentation: https://mdbootstrap.com/docs/jquery/forms/checkbox/

Please include a page showing possible form fields in your templates. Forms, along with links, are one of the primary foundations of the internet.