body, html {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
}
.fullscreen-gif {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
  background-color: black;
  overflow: hidden;
}
.fullscreen-gif img {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  object-fit: cover;
}