body {
    background: url(../../image/@.jpg) no-repeat center fixed;
    -webkit-background-size: cover;
    background-size: cover;
    margin: auto;
}

#form {

    width: 350px;

    height: auto;

    position: absolute;

    left: 50%;

    top: 50%;

    transform: translate(-50%, -50%);

    -webkit-transform: translate(-50%, -50%);
}

input, #message {    border: 3px solid blue;
}