html {
    color: #222;
    font-size: 1em;
    line-height: 1.4;
}

#bg {
    position: fixed; top: 0%; left: 0%; width: 100%; height: 100%;
}

#bg #back {
    position: absolute; top: 0; left: 0; right: 0; bottom: 0; margin: auto; min-width: 10%; min-height: 10%; width: 100%;
}

#bg #btn {
    position: absolute; left: 50%; transform: translate(-50%, 30%); background-color: transparent; width: 40%; display: flex; justify-content: center;
}

@media (min-width: 250px) {

    #bg #back {
        width: 100%;
    }
    #bg #btn {
        bottom: calc(100% - 60vh);
    }
    #img{
        width: 100%;
        height: 100%;
    }
}

@media (min-width: 540px) {
  
    #bg #btn {
        bottom: 35%;
    }
    #img{
        width: 80%;
        height: 68%;
    }
}

@media (min-width: 1025px) {
  
    #bg #btn {
        bottom: 10%;
    }
    #img{
        width: 70%;
        height: 70%;
    }
}