RocketChat/Rocket.Chat

.emoji {
    position: relative;

    display: inline-block;
    overflow: hidden;

    width: 1.375rem;
    height: 1.375rem;
    margin: 0 0.15em;

    vertical-align: middle;
    white-space: nowrap;
    text-indent: 100%;

    background-repeat: no-repeat;
    background-position: center;
    background-size: contain;

    font-size: inherit;
    line-height: normal;
    image-rendering: auto;
}