#btn-start-stop {
    display: flex;
    flex-direction: row;
    flex-wrap: nowrap;
    align-content: center;
    align-items: center;
    justify-content: center;
    margin: 0 auto;
}

#btn-start-stop .image {
    width: 24px;
    height: 24px;
    background-color: black;
    display: inline-block;
    -webkit-mask: url(../resources/play.svg) no-repeat center;
    mask: url(../resources/play.svg) no-repeat center;
    margin-right: 4px;
}

    #btn-start-stop .image.started {
        -webkit-mask: url(../resources/stop.svg) no-repeat center;
        mask: url(../resources/stop.svg) no-repeat center;
    }