html
{margin: 0;
padding: 0;}

h1
{background-color: BLACK;
color: #00FF00;
text-align: CENTER}


.submit
{background-color: #3fb6b2;
padding:12px 45px;
border-radius: 5px;
cursor: pointer;
color: #ffffff;
margin-left: 35%;
font-weight: bold;}

html { 
  margin:0;
  padding:0;
  background: url("https://www.sohealthy.fr/wp-content/uploads/2019/09/Escalade-chamonix3.jpg") no-repeat center fixed; 
  -webkit-background-size: cover; 
  background-size: cover;
}