body{
            background-size: cover;
            background-repeat: no-repeat;
           background-color: black;
        }
        .leftside{
            left: 0px;
            width: 300px;
            height: 800px;
            background-color: grey;
            visibility: hidden;
            margin: auto;
float: left;
           }
           .rightside{
            width: 300px;
            height: 800px;
            background-color: grey;
            visibility: hidden;
            margin: auto;
float: right; 
}
        .block{
            background-color: grey;
             width: 600px;
             height: 800px;
             visibility: hidden;
             margin: auto;
             float: none;
            
        }
        #block{
               -webkit-animation-duration: 1s;
            animation-duration: 1s;
            -webkit-animation-fill-mode: both;
            animation-fill-mode: both;
            }
        .welcome{
           display: block;
  margin-left: auto;
  margin-right: auto;
  width: 10%;
  -webkit-animation-duration: 1s;
            animation-duration: 1s;
            -webkit-animation-fill-mode: both;
            animation-fill-mode: both;
        }
        @-webkit-keyframes fadeOut {
            0% {
                opacity: 1;
            }

            100% {
                opacity: 0;
            }
        }

        @keyframes fadeOut {
            0% {
                opacity: 1;
            }

            100% {
                opacity: 0;
            }
        }
        @-webkit-keyframes fadeIn {
            0% {
                opacity: 0;
            }

            100% {
                opacity: 1;
            }
        }

        @keyframes fadeIn {
            0% {
                opacity: 0;
            }

            100% {
                opacity: 1;
            }
        }

        .fadeOut {
            -webkit-animation-name: fadeOut;
            animation-name: fadeOut;
        }
                .fadeIn {
            -webkit-animation-name: fadeIn;
            animation-name: fadeIn;
        }