body {
  background: url(https://i.pinimg.com/originals/8e/ff/81/8eff81d46686e3c82c64565eb09393b9.gif) repeat;
}

.mainbox {
  display: flex;
  justify-content: center;
  transform: translate(0%, 100%);
}

h1 {
width: 1200px; 
  padding: 10px;
  background: purple;
  color: #fff;
  font-weight: bold;
  font-family: lucida console;
}