我想要一个切换div elemenet，用z-index重叠底层内容。我怎样才能做到这一点？

I have a short intro text inside a box, if the user wants to read futrher he can toggle a hidden div element that shows the rest of the content. Under this intro box I have some other element, which I always want to stay in that position. I want the toggled text to 'show above' the fixed content, and I don't want it to push downwards when the toggled div is opened. I've experimented with various z-index values, absolute and relative positioning, to no avail. Is there a clean CSS based solution to this? Please help! Here's a demo of what I'm trying to do:I have a short intro text inside a box, if the