.bubble{
    position: relative;
    background-color: rgba(255, 255, 255, 0.5);
    border-radius: .4em;
}

.bubble::after {
    content: '';
    position: absolute;
    top: 0;
    left: 50%;
    width: 0;
    height: 0;
    border: 10px solid transparent;
    border-bottom-color: rgba(255, 255, 255, 0.5);
    border-top: 0;
    margin-left: -10px;
    margin-top: -10px;
}