html, body {
  margin: 0;
  padding: 0;
  background: #000;
  min-width: 320px;
}
#parent {
  display: flex;
  align-items: center;
margin: auto;
  width: 100%;
height: 100vh;
    max-width: 800px;
  min-width: 320px;
  
}
#child {
  text-align: center;
}
img {
  width: 100%;
}
h1 {
  font-family: Arial, Helvetica, sans-serif;
  font-size: 48px;
  margin: 0;
  color: #fff;
}