#scrollToTopBtn {
    position: fixed;
    bottom: 150px;
    left: 50%;
    margin-left: calc(var(--content-width, 800px) / 2 + 40px);
    width: 60px;
    height: 60px;
    background: var(--main-gradient);
    color: white;
    border: none;
    border-radius: 50%;
    cursor: pointer;
    box-shadow: 0 4px 12px rgba(55, 185, 195, 0.4);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
    transition: all 0.3s ease;
    opacity: 0;
    transform: translateY(20px) translateX(-50%);
    font-size: 24px;
}
#scrollToTopBtn.show {
    opacity: 1;
    transform: translateY(0) translateX(-50%);
}
#scrollToTopBtn:hover {
    background: var(--accent-gradient);
    box-shadow: 0 6px 16px rgba(55, 185, 195, 0.6);
    transform: translateY(-3px) translateX(-50%);
}
#scrollToTopBtn:active {
    transform: scale(0.95) translateX(-50%);
}
@media (max-width: 1200px) {
    #scrollToTopBtn {
        margin-left: calc(min(800px, 90vw) / 2 + 20px);
    }
}
@media (max-width: 900px) {
    #scrollToTopBtn {
        right: 20px;
        left: auto;
        margin-left: 0;
        transform: translateY(20px);
    }

    #scrollToTopBtn.show {
        transform: translateY(0);
    }

    #scrollToTopBtn:hover {
        transform: translateY(-3px);
    }

    #scrollToTopBtn:active {
        transform: scale(0.95);
    }
}
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px) translateX(-50%);
    }
    to {
        opacity: 1;
        transform: translateY(0) translateX(-50%);
    }
}
#scrollToTopBtn.show {
    animation: fadeInUp 0.3s ease forwards;
}