html {margin: 0; 
   padding: 0; 
   background-image: url(../img/wallpaper-main.png);
   background-repeat: no-repeat;
   background-size: cover;
   background-attachment: fixed;
   overflow-x: hidden;
  }
 
 div {
   margin: 20px;
 }
  
 ul {
   list-style-type: none;
   width: 100%;
 }

.hide {
  visibility: hidden !important;
}


h1 {
  text-align: center;
}