function Popup(){
  this.modal = document.querySelector('.modal');
  this.overlay = document.querySelector('.overlay');

  var popup = this;
  this.open =function(content){
    popup.modal.innerHTML = content;
    popup.overlay.classList.add('open');
    popup.modal.classList.add('open');
  };
  this.close =function(){
    popup.overlay.classList.remove('open');
    popup.modal.classList.remove('open');
  };

  this.overlay.onclick = popup.close;

}
window.onload = function(){
  var p = new Popup();

  document.querySelector('.callme').onclick = function(){
    var form = document.querySelector('.for-callme-popup');
    p.open(form.innerHTML);
  };
  document.querySelector('.write').onclick = function(){
    p.open('заказ звонка');
  };
}