someMask.css

.mask{
    position: fixed;
    left: 0;
    top: 0;
    bottom: 0;
    right: 0;
    z-index: 9999;
    overflow: hidden;
    background-color: rgba(61, 67, 76, 0.7);
    background-image: -webkit-radial-gradient(rgba(0, 0, 0, 0) 10%,rgba(0, 0, 0, 0.6));
    background-image: radial-gradient( rgba(0, 0, 0, 0) 10%,rgba(0, 0, 0, 0.6));
    opacity: 0;
    pointer-events: none;
    -webkit-transition: 250ms opacity linear;
    -moz-transition: 250ms opacity linear;
    transition: 250ms opacity linear;
}