# How Do I Draw Two Overlapping Rectangles?

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:

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}

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

or

or

For the last picture I use the following code:

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

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

In code I use TikZ library shadows.

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Here is one way without tikz. The \rule dimensions and the first argument of \stackengine will allow different box sizes and offsets.

In this case, the boxes are 30pt x 30pt, with a 4pt horizontal offset and 3pt vertical offset. The box rule thickness is the default \fboxrule.

\documentclass[12pt]{article}
\usepackage{xcolor,stackengine}
\fboxsep=-\fboxrule
\begin{document}
\stackengine{3pt}{\rule{4pt}{0pt}\fbox{\textcolor{white}{\rule{30pt}{30pt}}}}
{\fbox{\textcolor{white}{\rule{30pt}{30pt}}}}
{O}{l}{F}{F}{L}
\end{document}

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