.mfp-container {
  overflow: hidden;
}
.mfp-img {
  padding: 0 !important;
}
.mfp-close {
  top: 0 !important;
  right: 0 !important;
  width: 44px !important;
  height: 44px !important;
  padding: 0 !important;
  background-color: #000 !important;
  text-align: center !important;
}

#demo-section h3, #demo-section p {
  font-family: sans-serif;
  text-align: center;
}
#demo-section .popup-gallery {
  display: grid;
  grid-template-columns: 1fr 1fr;
  grid-column-gap: 0;
}
@media screen and (min-width: 600px) {
  #demo-section .popup-gallery {
    grid-template-columns: 1fr 1fr 1fr 1fr;
  }
}
#demo-section .popup-gallery a {
  box-sizing: border-box;
  padding: 0.5em;
  width: 100%;
}
#demo-section .popup-gallery a img {
  width: 100%;       /* Was 100% - Changed to auto  */
  height: auto;      /* Was auto - Changed to 100%  */
}

#myBtn {
  display: none;
  position: fixed;
  text-align: center;
  bottom: 20px;
  /* right: 30px; */
  left: 50%;
  transform: translateX(-50%);
  z-index: 99;
  font-size: 18px;
  border: none;
  outline: none;
  background-color: #ffff00;
  color: black;
  cursor: pointer;
  padding: 15px;
  border-radius: 4px;
}

#myBtn:hover {
  background-color: #ff9933;
}