#customPopup {
  position: fixed;
  inset: 0;                 /* top:0 left:0 right:0 bottom:0 */
  background: rgba(0,0,0,0.75);
  display: none;
  justify-content: center;
  align-items: center;
  z-index: 2147483647;      /* Maximum possible */
}

.popup-box {
  position: relative;
  width: 90%;
  max-width: 650px;
}

.popup-box img {
  width: 100%;
  border-radius: 8px;
  display: block;
}

.close-btn {
  position: absolute;
  top: -12px;
  right: -12px;
  background: #fff;
  width: 35px;
  height: 35px;
  border-radius: 50%;
  text-align: center;
  line-height: 35px;
  font-size: 22px;
  cursor: pointer;
  font-weight: bold;
}