.mui-popover {
    width: 50%;
    height: 50%;
    position: fixed;
    border-radius: 0;
    left: 50% !important;
    top: 50% !important;
    margin: 0 auto !important;
    z-index: 9999;
    background-color: #fff;
    -webkit-transform: translateX(-50%) translateY(-50%);
    -moz-transform: translateX(-50%) translateY(-50%);
    -ms-transform: translateX(-50%) translateY(-50%);
    transform: translateX(-50%) translateY(-50%);
}

    .mui-popover .mui-popover-arrow:after {
        width: 0px;
    }