/* Back to Top Button */
.back-to-top {
    position: fixed;
    bottom: 30px;
    right: 30px;
    width: 70px;
    height: 70px;
    background: transparent;
    border: none;
    border-radius: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    z-index: 999;
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.3s ease, visibility 0.3s ease;
    box-shadow: none;
    padding: 0;
}

.back-to-top.show {
    opacity: 1;
    visibility: visible;
}

.back-to-top:hover {
    transform: none;
    box-shadow: none;
}

.back-to-top::before {
    content: '';
    width: 100%;
    height: 100%;
    background-image: url('../切图/广告平台标准/Top-正常.png');
    background-size: contain;
    background-position: center;
    background-repeat: no-repeat;
    transition: background-image 0.2s ease;
}

.back-to-top:hover::before,
.back-to-top:active::before {
    background-image: url('../切图/广告平台标准/Top-点击.png');
}

/* Responsive */
@media screen and (max-width: 1920px) {
    .back-to-top {
        bottom: 1.56vw; /* 30/1920 */
        right: 1.56vw; /* 30/1920 */
        width: 3.65vw; /* 70/1920 */
        height: 3.65vw; /* 70/1920 */
        border-radius: 1.04vw; /* 20/1920 */
    }
    
    .back-to-top::before {
        /* Image scales with button size */
    }
}

@media screen and (max-width: 768px) {
    .back-to-top {
        bottom: 20px;
        right: 20px;
        width: 50px;
        height: 50px;
        border-radius: 15px;
    }
    
    .back-to-top::before {
        /* Image scales with button size */
    }
}