My knowledge of TikZ is very limited. I'm drawing Venn diagrams of this style in my document:
\begin{figure}[H]
\centering
\begin{tikzpicture}
\def\firstcircle{(0,0) circle (1.5cm)}
\def\secondcircle{(0:2cm) circle (1.5cm)}
\colorlet{circle edge}{red!50}
\colorlet{circle area}{red!20}
\tikzset{filled/.style={fill=circle area, draw=circle edge, thick},
outline/.style={draw=circle edge, thick}}
\setlength{\parskip}{5mm}
\begin{scope}
\clip \firstcircle;
\fill[filled] \secondcircle;
\end{scope}
\draw[outline] \firstcircle node {$M_1$};
\draw[outline] \secondcircle node {$M_2$};
\node[anchor=south] at (current bounding box.north) {$M_1 \cap M_2$};
\end{tikzpicture}
\end{figure}
Now, I want to draw a set complement see this one on Wikipedia, so I need to draw a box around it and fill it with some colour. The operation should be on top of the picture (like in the previous diagram). Does anybody know how to do that in the same kind of general style like the first diagram?
Thank you!

