Checkbox not showing once checked on our website

I am trying to get the checked checkbox to show up on our website. At the bottom of this page: https://www.shiftdivorceguide.com/submit-listing/ we have two check boxes, "I agree" and "Already have an account".

When I check them they disappear and I want them to show with a check mark in them.

HTML <input id="policycheck" type="checkbox" name="policycheck" value="true">

CSS:

.checkbox input[type=checkbox] {
    display: none;
}

If I change this to to display:inline a second smaller box displays and if I check it on I Agree it jumps to the right.

I would like the nicer larger box (not the smaller box) to remain and show as checked when someone checks it.

Can anyone point me in the right direction on how to fix this?

Thanks in advance!