<div class="container text-center">
        <button class="btn btn-default ripple btn-lg">Button</button>
        <button class="btn btn-default ripple btn-lg">Button with very long content</button>
</div>

.ripple {
    position: relative;
/*     隐藏溢出的径向渐变背景 */
    overflow: hidden;
}

.ripple:after {
    content: "";
    display: block;
    position: absolute;
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    pointer-events: none;
/*     设置径向渐变 */
    background-image: radial-gradient(circle, #666 10%, transparent 10.01%);
    background-repeat: no-repeat;
    background-position: 50%;
    transform: scale(10, 10);
    opacity: 0;
    transition: transform .3s, opacity .5s;
}

.ripple:active:after {
    transform: scale(0, 0);
    opacity: .3;
/*     设置初始状态 */
    transition: 0s;
}