function show_login_form() {
    document.getElementById('login_form_container').style.visibility = 'visible';
    document.getElementById('address_form_container').style.visibility = 'hidden';
}

function show_reg_form() {
    document.getElementById('login_form_container').style.visibility = 'hidden';
    document.getElementById('address_form_container').style.visibility = 'visible';
}