:root {
    --fc-button-bg-color: #777;
    --fc-button-border-color: #777;
    --fc-button-active-bg-color: #333;
    --fc-button-active-border-color: #333;
    --fc-button-hover-bg-color: #333;
    --fc-button-hover-border-color: #333;    
}
.fc .fc-button-primary:focus, .fc .fc-button-primary:not(:disabled).fc-button-active:focus, .fc .fc-button-primary:not(:disabled):active:focus{
    box-shadow:none;
}