odoo-mobile/www/lib/ionic-material/src/scss/elements/mask.scss

/* Mask
==================================*/

.hero.has-mask:after, .item.has-mask:after, .card.has-mask:after {
    content: '';
    background: -webkit-linear-gradient(top, rgba(0, 0, 0, 0) 0%, rgba(0, 0, 0, 0.6) 100%);
    height: 100%;
    left: 0;
    position: absolute;
    top: 0;
    z-index: 0;
    width: 100%;
}
.hero.has-mask-reverse:after, .item.has-mask-reverse:after, .card.has-mask-reverse:after {
    content: '';
    background: -webkit-linear-gradient(top, rgba(0, 0, 0, 0.6) 0%, rgba(0, 0, 0, 0) 100%);
    height: 100%;
    left: 0;
    position: absolute;
    top: 0;
    z-index: 0;
    width: 100%;
}