.bottom-section,
.top-section {
    position: fixed;
    left: 0;
    right: 0;
    z-index: 100;
}

body,
html {
    margin: 0;
    padding: 0;
    height: 100%;
    font-family: Arial, sans-serif;
}

.wrapper {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.section-wrapper {
    max-width: 750px;
    width: 100%;
    margin: 0 auto;
}

.top-section {
    top: 0;
}

.bottom-section .section-wrapper,
.top-section .section-wrapper {
    display: flex;
    justify-content: center;
}

.bottom-img,
.gallery-img,
.top-img {
    width: 100%;
    max-width: 750px;
    height: auto;
    display: block;
}

.middle-section {
    flex: 1;
    padding-top: var(--top-height, 0px);
    padding-bottom: var(--bottom-height, 0px);
}

/* 主图容器：让按钮以主图为定位范围 */
.photo-gallery {
    width: 100%;
    position: relative;
}

/* 主图右上角 100x100 图片按钮 */
.image-top-btn {
    position: absolute;
    top: 5px;
    right: 30px;
    width: 60px;
    height: 60px;
    z-index: 9999;
    display: block;
}

.image-top-btn img {
    width: 100%;
    height: 100%;
    display: block;
    object-fit: cover;
}

.bottom-section {
    bottom: 0;
}

@media (min-width: 769px) {
    .bottom-img,
    .gallery-img,
    .section-wrapper,
    .top-img {
        max-width: 500px;
    }
}