.stb-btn {
    position: fixed;
    bottom: 40px;
    width: 50px;
    height: 50px;
    background: #000;
    color: #fff;
    font-size: 22px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    border-radius: 50%;
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.3s ease, transform 0.3s ease;
    z-index: 9999;
}

.stb-btn.visible {
    opacity: 0.85;
    visibility: visible;
}

#stb-scroll-top {
    right: 30px;
}

#stb-back-nav {
    left: 30px;
}

.stb-btn:hover {
    opacity: 1;
    transform: scale(1.1);
}