.scrollToTopBtn {
    background-color: #a6192e;
    border: none;
    color: white;
    cursor: pointer;
    font-size: 2rem;
    width: 48px;
    height: 48px;
    display: flex;
    justify-content: center;
    align-items: center;

    /* place it at the bottom right corner */
    position: fixed;
    bottom: 100px;
    right: 20px;
    /* keep it at the top of everything else */
    z-index: 100;
    /* hide with opacity */
    opacity: 0;
    /* also add a translate effect */
    transform: translateX(100px);
    /* and a transition */
    transition: all 0.5s ease;
}

.showBtn {
    opacity: 1;
    transform: translateX(0);
}