html {
    background: url(/images/sudouestsecurite/metal_maison.png) no-repeat center center fixed; 
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
}

body {
    display: flex;
    min-height: 100vh;
    flex-direction: column;
  }

.section{
    margin: 50px 0 50px 0;
}