#msgerreur{
    display: block;
    position: fixed;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    background-color: rgba(0, 0, 0, 0.5);
    z-index: 1000;
}

.popup_block{
    background: #fff;
    padding: 20px;
    border: 20px solid #ddd;
    position: relative;
    margin: 10% auto;
    width: 20%;
    box-shadow: 0px 0px 20px #000;
    border-radius: 10px;
}
img.btn_close {
    float: right;
    margin: -55px -55px 0 0;
}