How can I make a picture like this?

Question

I want to make a document with exercises and solutions in a breakable box like this picture:

Here is a minimal example which reproduces my problem :

\documentclass[12pt,a4paper,twoside,openright]{book}
\usepackage[utf8]{inputenc}
\usepackage[frenchb]{babel}
\usepackage[most]{tcolorbox}
\usepackage{multicol}
\usepackage{lipsum}
\usepackage{geometry}
\usepackage{etoolbox}
\definecolor{tcbcolback}{RGB}{255,128,0}

 \usepackage{varwidth}
\newtcolorbox{mybox}[2][]{enhanced,
    before skip=2mm,after skip=2mm,
    colback=black!5,colframe=black!50,boxrule=0.2mm,
    attach boxed title to top left={xshift=1cm,yshift*=1mm-\tcboxedtitleheight},
    varwidth boxed title*=-3cm,boxrule=1pt,breakable,colframe=green!75!black,drop lifted shadow,
    boxed title style={frame code={
            \path[fill=tcbcolback!60!black]
            ([yshift=-1mm,xshift=-1mm]frame.north west)
            arc[start angle=0,end angle=180,radius=1mm]
            ([yshift=-1mm,xshift=1mm]frame.north east)
            arc[start angle=180,end angle=0,radius=1mm];
            \path[left color=tcbcolback!90!black,right color=tcbcolback!90!black,
            middle color=tcbcolback!99!black]
            ([xshift=-2mm]frame.north west) -- ([xshift=2mm]frame.north east)
            [rounded corners=1mm]-- ([xshift=1mm,yshift=-1mm]frame.north east)
            -- (frame.south east) -- (frame.south west)
            -- ([xshift=-1mm,yshift=-1mm]frame.north west)
            [sharp corners]-- cycle;
        },interior engine=empty,
    },
    fonttitle=\bfseries,
    title={#2},#1}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\NewTColorBox[auto counter,number within=chapter]{exercise}{m+O{}}{%
    enhanced,
    colframe=green!20!black,
    colback=yellow!10!white,
    coltitle=green!40!black,
    fonttitle=\bfseries,
    underlay={\begin{tcbclipinterior}
            \shade[inner color=green!80!yellow,outer color=yellow!10!white]
            (interior.north west) circle (2cm);
            \draw[help lines,step=5mm,yellow!80!black,shift={(interior.north west)}]
            (interior.south west) grid (interior.north east);
    \end{tcbclipinterior}},
    title={Exercise~ \thetcbcounter:},
    label={exercise:#1},
    attach title to upper=\quad,
    after upper={\par\hfill\textcolor{green!40!black}%
        {\itshape Solution on page~\pageref{solution:#1}}},
    lowerbox=ignored,
    savelowerto=solutions/exercise-\thetcbcounter.tex,
    record={\string\solution{#1}{solutions/exercise-\thetcbcounter.tex}},
    #2
}

\NewTotalTColorBox{\solution}{mm}{%
    enhanced,
    colframe=red!20!black,
    colback=yellow!10!white,
    coltitle=red!40!black,
    fonttitle=\bfseries,
    underlay={\begin{tcbclipinterior}
            \shade[inner color=red!50!yellow,outer color=yellow!10!white]
            (interior.north west) circle (2cm);
            \draw[help lines,step=5mm,yellow!80!black,shift={(interior.north west)}]
            (interior.south west) grid (interior.north east);
    \end{tcbclipinterior}},
    title={Solution of Exercise~\ref{exercise:#1} on page~\pageref{exercise:#1}:},
    phantomlabel={solution:#1},
    attach title to upper=\par,
}{\input{#2}}

\tcbset{no solution/.style={no recording,after upper=}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{document}
\begin{mybox}[]{Exercises }
\begin{exercise}{Ex1}[coltitle=cyan!80!black]
        \lipsum[1-6]
\end{exercise}  
\end{mybox}
\end{document}

Answer 1

I think that I find the solution (I'm not sure that this solution works for all the shots), just add : "enforce breakable,pad at break=0mm,break at=-20pt" in the code of the inner box and everything goes in the right order, this is a minimal example :

\documentclass[12pt,a4paper,oneside,openright]{book}
\usepackage[utf8]{inputenc}
\usepackage[frenchb]{babel}
\usepackage[most]{tcolorbox}
\usepackage{multicol}
\usepackage{lipsum}
\usepackage{geometry}

\usepackage{etoolbox}
\definecolor{tcbcolback}{RGB}{255,128,0}

 \usepackage{varwidth}
\newtcolorbox{mybox}[2][]{enhanced,
    before skip=0mm,after skip=0mm,
    colback=black!5,colframe=black!50,boxrule=0.2mm,
    attach boxed title to top left={xshift=1cm,yshift*=1mm-\tcboxedtitleheight},
    varwidth boxed title*=-3cm,boxrule=1pt,breakable,pad at break*=0mm,colframe=green!75!black,drop lifted shadow,
    boxed title style={frame code={
            \path[fill=tcbcolback!60!black]
            ([yshift=-1mm,xshift=-1mm]frame.north west)
            arc[start angle=0,end angle=180,radius=1mm]
            ([yshift=-1mm,xshift=1mm]frame.north east)
            arc[start angle=180,end angle=0,radius=1mm];
            \path[left color=tcbcolback!90!black,right color=tcbcolback!90!black,
            middle color=tcbcolback!99!black]
            ([xshift=-2mm]frame.north west) -- ([xshift=2mm]frame.north east)
            [rounded corners=1mm]-- ([xshift=1mm,yshift=-1mm]frame.north east)
            -- (frame.south east) -- (frame.south west)
            -- ([xshift=-1mm,yshift=-1mm]frame.north west)
            [sharp corners]-- cycle;
        },interior engine=empty,
    },
    fonttitle=\bfseries,
    title={#2},#1}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\NewTColorBox[auto counter,number within=chapter]{exercise}{m+O{}}{%
    enhanced jigsaw,enforce breakable,pad at break=0mm,break at=-20pt,
    colframe=green!20!black,
    colback=yellow!10!white,
    coltitle=green!40!black,
    fonttitle=\bfseries,
    underlay={\begin{tcbclipinterior}
            \shade[inner color=green!80!yellow,outer color=yellow!10!white]
            (interior.north west) circle (2cm);
            \draw[help lines,step=5mm,yellow!80!black,shift={(interior.north west)}]
            (interior.south west) grid (interior.north east);
    \end{tcbclipinterior}},
    title={Exercise~ \thetcbcounter:},
    label={exercise:#1},
    attach title to upper=\quad,
    after upper={\par\hfill\textcolor{green!40!black}%
        {\itshape Solution on page~\pageref{solution:#1}}},
    lowerbox=ignored,
    savelowerto=solutions/exercise-\thetcbcounter.tex,
    record={\string\solution{#1}{solutions/exercise-\thetcbcounter.tex}},
    #2
}

\NewTotalTColorBox{\solution}{mm}{%
    enhanced,
    colframe=red!20!black,
    colback=yellow!10!white,
    coltitle=red!40!black,
    fonttitle=\bfseries,
    underlay={\begin{tcbclipinterior}
            \shade[inner color=red!50!yellow,outer color=yellow!10!white]
            (interior.north west) circle (2cm);
            \draw[help lines,step=5mm,yellow!80!black,shift={(interior.north west)}]
            (interior.south west) grid (interior.north east);
    \end{tcbclipinterior}},
    title={Solution of Exercise~\ref{exercise:#1} on page~\pageref{exercise:#1}:},
    phantomlabel={solution:#1},
    attach title to upper=\par,
}{\input{#2}}

\tcbset{no solution/.style={no recording,after upper=}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{document}
\begin{mybox}[]{Exercises }
\begin{exercise}{Ex1}[coltitle=cyan!80!black]
        \lipsum[1-6]
\end{exercise}  
\end{mybox}
\section{sec}
\lipsum[1-6]
\end{document}