.btn_beat {
    animation: btn-scale 4s linear infinite;
}
@keyframes btn-scale{
    0%{
        transform: scale(1) ;
    }
    12.5%{
        transform: scale(1.08) ;
    }
    25%{
        transform: scale(1) ;
    }
    37.5%{
        transform: scale(1.08) ;
    }
    50%{
        transform: scale(1) ;
    }
    100%{
        transform: scale(1) ;
    }
}