在彩色背景div顶部不可见的伪元素

I want to render a photo stack. I used a div with the before- and after-pseudo-elements. This works fine. Only caveat is: this div should be rendered on top of some unicolor background. So I place this div inside another div, which has the background color set. Now, the pseudo-elements are not visible anymore. What is going wrong?I want to render a photo stack. I used a div wi