* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
*::after {
  box-sizing: border-box;
}
*::before {
  box-sizing: border-box;
}
#demo {
  word-break: break-all;
}
#div1 {
  position: fixed;
  left: 50%;
  transform: translateX(-50%);
  top: 20px;
}
#div1::before {
  content: "";
  display: block;
  position: absolute;
}
#div1::after {
  content: "";
  display: block;
  position: absolute;
}
@media (max-width: 500px) {
  #html {
    height: 50vh;
    overflow: auto;
  }
  #div1Wrapper {
    height: 50vh;
  }
  #div1 {
    position: relative;
    top: 0;
    right: 0;
  }
}