body.modal-open {
  visibility: hidden;
  height: 400vh;
}

body.modal-open .modal .modal-header,
body.modal-open .modal .modal-body {
  visibility: visible;
  position: absolute;
  left: 0;
  top: 0;
  margin: 0;
  padding: 0;
  width: auto;
  height: auto;
  overflow: visible !important;
}