#top-btn {
    visibility: hidden;
    overflow: visible;

    width: 0;
    height: 0;
    position: absolute;

    /* Change Size */
    font-size: 16px;
}

#top-btn > button {
    display: flex;
    align-items: center;
    justify-content: center;
    visibility: visible;

    width: 2.5em;
    height: 2.5em;
    position: fixed;
    right: 1.5em;
    bottom: 5em;

    border: none;
    border-radius: 0.4em;

    font-size: 0.8em;
    font-weight: bold;

    color: #FFF;
    background-color: rgba(0, 0, 0, 0.35);

    transition: all 200ms ease-in-out;
}

#top-btn > button.active {
    transform: scale(1.5);

    color: #FFF;
    background-color: rgba(255, 0, 150, 0.6);
    box-shadow:
      0 0.75em 1.875em rgba(0, 0, 0, 0.5),
      0 0 0.9375em rgba(255, 0, 150, 0.7
    );

    transform-origin: center center;
}