/* 背景オブジェクトのCSS */
/* object_containerで囲む場合 */
.object_container img {
    opacity: 0;
    transform: translateY(30px);
    transition: all 0.5s 0.5s ease;
}
/* imgタグそのものにclassを付ける場合 */
img.object_container {
    height: auto;
    object-fit: contain;
    position: absolute;
    z-index: -1;
    opacity: 0;
    transform: translateY(30px);
    transition: all 0.5s 0.5s ease;
}

/* 発火後 */
.object_container.show img {
    opacity: 1;
    transform: translateY(0);
}
img.object_container.show {
    opacity: 1;
    transform: translateY(0);
}