button, a {
    position: relative;
    overflow: hidden;
    outline: none;
    border: 0;
    transition: background 400ms;
}

.btn.active.focus, .btn.active:focus, .btn.focus, .btn.focus:active, .btn:active:focus, .btn:focus {
    outline: 0;
    outline-offset: 0;
    background-image: none;
    -webkit-box-shadow: none;
    box-shadow: none;
}

.accordion-item, .accordion-item:focus, .accordion-item:active,
.accordion-header, .accordion-header:focus, .accordion-header:active,
.accordion-button, .accordion-button:focus, .accordion-button:active {
    outline: 0;
    outline-offset: 0;
    background-image: none;
    -webkit-box-shadow: none;
    box-shadow: none;
}

span.ripple {
    position: absolute;
    background: #fff;    
    transform: translate(-50%, -50%);
    pointer-events: none;
    border-radius: 50%;
    animation: ripple 1s linear infinite;
}

@keyframes ripple {
    0% {
        width: 0;
        height: 0;
        opacity: 0.5;
    }

    100% {
        width: 500px;
        height: 500px;
        opacity: 0;
    }
}