.plotInfoBox{
    position:relative;
    background:#fff;
    border:1px solid #999;
    border-radius:6px;
    box-shadow:0 2px 10px rgba(0,0,0,.3);
}

.plotInfoBox .arrow{
    position:absolute;
    bottom:-12px;
    left:45px;          /* Adjust according to your requirement */
    width:0;
    height:0;
    border-left:12px solid transparent;
    border-right:12px solid transparent;
    border-top:12px solid #fff;
}

.plotInfoBox .arrow:before{
    content:'';
    position:absolute;
    left:-13px;
    top:-14px;
    border-left:13px solid transparent;
    border-right:13px solid transparent;
    border-top:13px solid #999;
}