无论视口（响应）如何，在背景图像下定位DIV

I have a big background image of 1920x550px and I want to place a div directly under it. Since I don't know how to display the full image, I used a dirty trick and actually filled the image with a transparent part so it is a 1920x1080 image, then I display it with this:I have a big background image of 1920x550px and