Rocket.Chat/packages/rocketchat-colors/style.css

.message-color {
    display: inline-block;
    font-weight: 100;
}

.message-color-sample {
    width: 14px;
    height: 14px;
    display: inline-block;
    border-radius: 3px;
    margin-right: 3px;
    margin-left: 2px;
    border: 1px solid rgba(0,0,0,.2);
    position: relative;
    top: 2px;
}