Gmail ckeckbox and button

Is it possible to add a checkbox and a button that only enables when all the checkboxes are checked in a gmail?

I already have this:

Acepto los terminos y condiciones
Acepto la política de privacidad
Acepto las condiciones del sorteo

But I do not have the button as I do not know how to do it.

Can you help me?

(Moreover, I would like to have a big centered red button with white letters, but for now I only want to know how to make the button. If you can solve this too I would be so grateful)