various defined breakable boxes inside breakable box using overlapping

Question

This is follow-up question of my previous question tcolorbox: It is possible to put breakable boxes behind each other (overlap)?.

My question: how can I simulate various defined breakable boxes inside a breakable box by overlapping, so they seem to be inside each other? The defined boxes are for example

\newtcolorbox{}

Example would be

Answer 1

Following with the idea proposed in tcolorbox: It is possible to put breakable boxes behind each other (overlap)? this code proposes to declare three kind of boxes: topbox, middlebox and bottombox.

topbox must the first in the desired series, it contains and draws the outer title. After a topbox you can place as much as middlebox-es as you want and the series ends with a bottombox which will close the false outer tcolorbox.

middlebox draws outer lines and enlarges them to join previous topbox and following bottombox. It shows a wrong behaviour when the middle box is not broken and it's placed to the bottom of a page. I don't know how to solve it.

\documentclass{article}
\usepackage[most]{tcolorbox}
\usepackage{lipsum}

\newtcolorbox{topbox}[2][]{
    title=#2,
    enhanced, breakable, 
    enlarge top initially by=1cm,
%    enlarge bottom finally by=5mm,
    enlarge left by=5mm,
    enlarge right by=5mm,
    width=\linewidth-10mm,
    overlay unbroken and first={
        \draw[green!70!black, line width=.5mm, rounded corners]
            ([xshift=-5mm]frame.south west)|-([yshift=1cm]frame.north)-|
            ([xshift=5mm]frame.south east);
        \node[fill=green!70!black, minimum height=5mm, 
            minimum width=\linewidth, anchor=north] at ([yshift=1cm]frame.north) 
            (outertitle) {};
        \node[text=white, anchor=west] at ([xshift=3mm]outertitle.west) {Outer title};
        },
    overlay middle and last={
        \draw[green!70!black, line width=.5mm]
             ([xshift=-5mm]frame.north west)--([xshift=-5mm]frame.south west)
             ([xshift=5mm]frame.north east)--([xshift=5mm]frame.south east);
    },
    #1
}

\newtcolorbox{middlebox}[2][]{
    title=#2,
    enhanced, breakable, 
%    enlarge top initially by=1cm,
%    enlarge bottom finally by=5mm,
    enlarge left by=5mm,
    enlarge right by=5mm,
    width=\linewidth-10mm,
    overlay unbroken={
        \draw[green!70!black, line width=.5mm]
             ([shift={(-5mm,5mm)}]frame.north west)--([shift={(-5mm,-5mm)}]frame.south west)
             ([shift={(5mm,5mm)}]frame.north east)--([shift={(5mm,-5mm)}]frame.south east);
        },
    overlay first={
        \draw[green!70!black, line width=.5mm]
             ([shift={(-5mm,5mm)}]frame.north west)--([xshift=-5mm]frame.south west)
             ([shift={(5mm,5mm)}]frame.north east)--([xshift=5mm]frame.south east);
        },
    overlay middle={
        \draw[green!70!black, line width=.5mm]
             ([xshift=-5mm]frame.north west)--([xshift=-5mm]frame.south west)
             ([xshift=5mm]frame.north east)--([xshift=5mm]frame.south east);
    },
    overlay last={
        \draw[green!70!black, line width=.5mm]
             ([xshift=-5mm]frame.north west)--([shift={(-5mm,-5mm)}]frame.south west)
             ([xshift=5mm]frame.north east)--([shift={(5mm,-5mm)}]frame.south east);
    },
    #1
}

\newtcolorbox{bottombox}[2][]{
    title=#2,
    enhanced, breakable, 
%    enlarge top initially by=1cm,
    enlarge bottom finally by=5mm,
    enlarge left by=5mm,
    enlarge right by=5mm,
    width=\linewidth-10mm,
    overlay unbroken and last={
        \draw[green!70!black, line width=.5mm, rounded corners]
             ([xshift=-5mm]frame.north west)|-([yshift=-5mm]frame.south)
             -|([xshift=5mm]frame.north east);
        },
    overlay first={
        \draw[green!70!black, line width=.5mm]
             ([xshift=-5mm]frame.north west)--([xshift=-5mm]frame.south west)
             ([xshift=5mm]frame.north east)--([xshift=5mm]frame.south east);
        },
    overlay middle={
        \draw[green!70!black, line width=.5mm, rounded corners]
             ([xshift=-5mm]frame.north west)--([xshift=-5mm]frame.south west)
             ([xshift=5mm]frame.north east)--([xshift=5mm]frame.south east);
    },
    #1
}

\begin{document}
\lipsum[1]
\begin{topbox}{this is the title}
\lipsum[1-2]
\end{topbox}
\begin{middlebox}[colframe=red, colback=pink!10]{this is the title}
\lipsum[1-5]
\end{middlebox}
\begin{middlebox}[colframe=brown!70!black, colback=brown!10]{this is the title}
\lipsum[1-2]
\end{middlebox}
\begin{bottombox}[colframe=blue, colback=cyan!10]{this is the title}
\lipsum[1-3]
\end{bottombox}
\lipsum[1]
\end{document}