html{
    background-image:url("https://fondosmil.com/fondo/12854.jpg");
    }

body{
     text-align: center;
    width: 700px;
  margin: 200px auto;
    border-radius: 35px;

  border: 5px solid black;
 background:slategray;
     
}

button{
    background-color:darkgray; /* Green */
    border-radius: 8px;
    color: white;
    padding: 15px 32px;
    text-align: center;
    text-decoration: none;
    display: inline-block;
    font-size: 16px;
}