/* CSS layout */

html {
    background-image: linear-gradient(
    rgba(0, 0, 0, 0.2),
    rgba(0, 0, 0, 0.2)
    ), url('../img-web/Wirral_Sunset.jpg');
    background-repeat: no-repeat;
    background-attachment: fixed;
    background-size: cover;
}
div#left {
    float: left;
    width: 50%; 
}
div#right { 
    float: right;
    width: 50%;
}
.center {
  display: block;
  margin-left: auto;
  margin-right: auto;
}