#payOverlay {
  position: fixed; top:0; left:0; right:0; bottom:0;
  background: rgba(0,0,0,0.6); display:flex;
  align-items: center; justify-content: center;
  z-index: 10000;
}
#payOverlay .inner {
  background: #fff; padding: 20px; border-radius: 8px;
  max-width: 320px; width: 100%; text-align: center;
  box-shadow: 0 2px 10px rgba(0,0,0,0.2);
}
#payOverlay label { display:block; margin: 10px 0; }
#payOverlay button { margin-top: 15px; padding: 8px 16px; }