body {
  margin: 0;
  font-family: verdana;
  text-align: center;
}

body::before {
  content: "";
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: url("passarinho.jpg");
  background-size: 1500px;
  background-repeat: repeat;
  z-index: -1;
}

h1{
    border: black 3px dashed;
    width: 600px;
    margin: auto;
    margin-top: 15px;
  }

.box{
    background-color: white;
    width: 500px;
    height: auto;
    margin: auto;
    margin-top: 15px;
  }