body {
    background-image: url(images/z.png);
    background-size: cover;
    background-repeat: no-repeat;
    background-position: center;
    background-attachment: fixed;
    height: 100%;
}

.start {
    position: absolute;
    top: -2.5rem;
    left: 50%;
    margin-left: -50px;
    font-size: rem;
    font-weight: bold;
    color: #fff;
    background-color: red;
    border: 5px double #fff;
    border-radius: 14px;
    padding: 8px 10px;
    outline: none;
    letter-spacing: .05em;
    cursor: pointer;
    margin-top: 600px;
}

.start a {
    color: white;
    text-decoration: none;
}

@media (max-width: 680px) {
    body {
        background-size: contain!important;
        background-repeat: repeat-y;
        background-position: center;
        background-attachment: fixed;
        height: 100%;
        margin-top: 12px;
    }
    .start {
        top: -4.5em;
    }
}
@media (max-width:380px){
    .start{
        top: -13.5rem!important;
    }
}
@media (max-width:400px){
    body {
        background-size: contain!important;
        background-repeat: repeat-y;
        background-position: center;
        background-attachment: fixed;
        height: 100%;
        margin-top: 12px;
    }
    .start{
        top: -7.5rem!important;
    }
}
@media (max-width:1024px){
    .start{
        top: -17.5rem;
    }
}