Multistep form with radio and checkboxes

[nordberg60]

I'm trying to incorporate this great example for a multi step form but would like to add radio and checkboxes.

https://www.w3schools.com/howto/howto_js_form_steps.asp

I am using this custom checkbox and radio option:

https://www.w3schools.com/howto/howto_css_custom_checkbox.asp

Can someone help how to modify javascript code under the (validateForm function) or otherwise to require the checkboxes and radio buttons are selected?

I have tried countless options (I can't even remember everything I tried) but I am sure it is probably something simply.