.buble {
    position: absolute;
    bottom: -50px;
    width: 100px;
    height: 100px;
    background: transparent;
    border-radius: 50%;
    background-size: cover;
    pointer-events: none;
    box-shadow: inset 0 10px 10px rgba(255, 255, 255, 0.5);
    animation: animate 4s linear infinite;
}

.buble:before {
    content: "";
    position: absolute;
    width: 100%;
    height: 100%;
    transform: scale(0.25) translate(-70%, -70%);
    background: radial-gradient(#fff, transparent);
    border-radius: 50%;
}

@keyframes animate {
    0% {
        transform: translateY(-250%);
        opacity: 1;
    }

    60%,
    99% {
        opacity: 1;
    }

    100% {
        transform: translateY(-1200%);
        opacity: 0;
    }
}

body {overflow-x: hidden;}