body img {
    position: fixed;
    height: 100%;
    width: 100%;
    top: 0;
    left: 0;
}

.center-box {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%,-50%);
    background: rgba(255,255,255,0.7);
    padding: 20px 20px;
}

.center-box p {
    font-size: 27px;
    font-weight: bold;
}