CSS position absolute center

position-absolute-center.css

.container {
    width: 25%;
    height: 50px;
    position: relative;
}

.container .popup {
    position: absolute;    
    width: 300px;
    margin-left: 50%;
    left: -150px;
    bottom: 50px;
    background-color: #d77c7c;
    height: 100px;
}

.container .popup:after {
    content: "";
    position: absolute;
    top: 100%;
    left: 50%;
    margin-left: -5px;
    border-width: 5px;
    border-style: solid;
    border-color: #d77c7c transparent transparent transparent;
}