It’s important to structure something like this really carefully. Consider how this all will fit within the whole page. Assuming you want this full width, that’s fine, but because you want the search section associated with the slideshow, wrap them both in a shared container that is set to position: relative so that they can be positioned in relation to each other.
I would use just a background color on the search section so that you can set rgba transparency on it.
It’s actually quite easy to do, but as I mentioned, first things first. I made some suggestions about the initial structure. Did that make sense? Did you try it?