css mobil konusunda yardım

 width: 100%;
    max-width: 350px;
    height: 350px;
    background: url(xxx);
    display: flex;
    background-repeat: no-repeat;
    background-size: 350px;
    border-radius: 3px;
    justify-content: center;
    align-items: center;
    position: fixed;
    content: ".";
    font-size: 100%;
    color: transparent;
    font-weight: bold;
    left: 50%;
    transform: translate(-50%, -50%);
    top: 40%;
    z-index: 5;