.begin{
    width: 100vw;
    height: 100vh;
    background-color: white;
    position: fixed;
    opacity: 1;
}

.begin img{
    width: 100%;
    height: 100%;
}

.bk{
    background-image: url("https://static.igem.wiki/teams/4157/wiki/bk-home.png");
    background-size: 100%;
    background-repeat: repeat;
}
@keyframes revolve{

    0%{-webkit-transform:rotate(0deg);}

    50%{-webkit-transform:rotate(-180deg);}

    100%{-webkit-transform:rotate(-360deg);}
}