[Tex/LaTex] How Do I Draw Two Overlapping Rectangles

tikz-pgf

I'm working on an interaction diagram for a programming design course. For sets of objects, I am required to draw overlapping rectangles, roughly as such:

Example 1

There was a post on overlapping fills that seems pretty close to what I want, but I couldn't figure out how to use the style of my other rectangles.

Here's a minimal version of what I have:

\documentclass{article}

\usepackage{amssymb}
\usepackage{tikz}
\usetikzlibrary{positioning}

\title{Interaction Diagram - Add Book}
\author{}

\begin{document}

\begin{center}
\begin{tikzpicture}[
  auto,
  block/.style = {
    minimum width = 9em,
    rectangle,
    draw=black,
    align=center,
    rounded corners
  }
]
\node[block, below = 2cm of start]      (controller) {\underline{: SystemController}};
\node[block, below = 2cm of controller] (system)     {\underline{: System}}; 

% the following line should be the doubled up rectangles.
\node[block, below = 2cm of system] (books) {Books};

\end{tikzpicture}
\end{center}
\end{document}

Best Answer

I assume, that actually you like to have something like this:

enter image description here

or

enter image description here

or

enter image description here

For the last picture I use the following code:

\documentclass[tikz,
               border= 3mm]{standalone}
\usetikzlibrary{positioning,shadows}

\begin{document}
\begin{tikzpicture}[
book/.style = {rectangle, draw, rounded corners, fill= white, 
               text width=9em, align= center,
               copy shadow={draw, fill=gray, 
                            shadow xshift=0.5mm, shadow yshift=-0.5mm}
               }
                    ] 
\node[book] (books) {Books};
\end{tikzpicture}
\end{document}

In code I use TikZ library shadows.

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