Custom example environment with colorbox and vertical line for `kaobook` document class

Question

I am making a custom example environment for the kaobook class and would like to modify the second example environment from this question:

\usepackage{chngcntr}
\usepackage[tikz]{mdframed}
\usepackage{lipsum}
\definecolor{greentitle}{RGB}{61,170,61}
\definecolor{greentitleback}{RGB}{216,233,213}
\newcounter{mdexample}
\counterwithin{mdexample}{section}
\newenvironment{myexample}[1]
  {\stepcounter{mdexample}\begin{mdframed}[
    frametitle=#1,
    frametitlefont=\normalfont,
    topline=false,
    bottomline=false,
    rightline=false,
    linecolor=greentitleback,
    linewidth=2pt,
    singleextra={
      \node[
        overlay,
        outer sep=0pt,
        anchor=north east,
        text width=2.5cm,
        minimum height=4ex,
        fill=greentitleback,
        font=\color{greentitle}\sffamily\scshape
      ] at (O|-P) {example~\themdexample};
      },
    firstextra={
      \node[
        overlay,
        outer sep=0pt,
        anchor=north east,
        text width=2.5cm,
        minimum height=4ex,
        fill=greentitleback,
        font=\color{greentitle}\sffamily\scshape
      ] at (O|-P) {example~\themdexample};
      }
    ]
  }
  {\end{mdframed}}

I would like to modify the environment so that:

• I would like the green "Example" box to be on the right side of the vertical line, not in the margin.

• I would like there to be a gap between the green "Example" box and the vertical line, instead of being connected to the vertical line.

• I would also like there to be a "title" for the example, similar to this. (e.g. title: "Evaluating a Function")

If it helps, here is a link to the Overleaf project. Feel free to edit it.

---

Edit: Thank you Alan Xiang for your solution!

I am wondering if it is possible to share numbering with theorems and other kaoboxes? I tried to change \newcounter{examplecounter}\counterwithin{examplecounter}{section} to \numberwithin{kaocounter}{section} but this didn't work.

Thank you!

Answer 1

Let me know if this is what you are looking for. It also supports breaking the box across multiple pages.

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[skins,hooks,xparse,breakable]{tcolorbox}
\usepackage{xcolor}
\usepackage{chngcntr}
\usepackage{blindtext}
\usepackage{tikz}
\newcounter{examplecounter}
\counterwithin{examplecounter}{section}
\usetikzlibrary{calc}
\definecolor{greentitle}{RGB}{61,170,61}
\definecolor{greentitleback}{RGB}{216,233,213}
\definecolor{drakgreentitle}{RGB}{24,131,80}
\DeclareTColorBox{bookexample}{O{}}{
    enhanced,
    breakable,
    arc=0pt,
    boxrule=0pt,
    colback=white,
    before skip={2em}, % increase spacing before the env
    overlay unbroken and first={
        % draw box on the left
        \node[fill=greentitleback,
            font=\color{greentitle}\sffamily\bfseries\large,
            anchor=south west,
            xshift=2mm
        ] (titlebox) at (frame.north west) 
        {Exercise \refstepcounter{examplecounter}\theexamplecounter};
    % write title on the right
    \node[font=\color{drakgreentitle}\sffamily\large, 
    anchor=west
    ] at ($(titlebox.east)+(2mm,0mm)$) {#1};

    % draw the vertical line on the left
    \draw[draw=greentitleback, line width=2pt] 
        (titlebox.north west-|frame.north west)--(frame.south west);
},
overlay middle and last={
    \draw[draw=greentitleback, line width=2pt] 
        (frame.north west)--(frame.south west);
}
fonttitle=\color{greentitle}\sffamily\bfseries,

}
\DeclareTColorBox{genericbox}{m}{
    enhanced,
    breakable,
    arc=0pt,
    boxrule=0pt,
    colback=white,
    attach boxed title to top left,
    boxed title style={
        colback=white,
        colframe=white,
    },
    title={#1},
    fonttitle=\color{greentitle}\sffamily\bfseries\large
}
\begin{document}
\section{First Section}
\null
\begin{bookexample}[My Title]
\Blindtext[4]
\end{bookexample}
\begin{genericbox}{Solution}
\Blindtext[2]
\end{genericbox}
\section{Second Section}
\null
\begin{bookexample}[Another Title]
\Blindtext[4]
\end{bookexample}
\begin{genericbox}{Solution}
\Blindtext[2]
\end{genericbox}
% No title
\begin{bookexample}
\Blindtext[1]
\end{bookexample}
\end{document}

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[skins,hooks,xparse,breakable]{tcolorbox}
\usepackage{xcolor}
\usepackage{chngcntr}
\usepackage{blindtext}
\usepackage{tikz}

% comment this line during integration because kaocounter would have been declared
\newcounter{kaocounter}
% you may not need the line below as well if it has already been configured using other approaches
\counterwithin{kaocounter}{section}

\usetikzlibrary{calc}

\definecolor{greentitle}{RGB}{61,170,61}
\definecolor{greentitleback}{RGB}{216,233,213}
\definecolor{drakgreentitle}{RGB}{24,131,80}

\DeclareTColorBox{bookexample}{O{}o}{
    enhanced,
    breakable,
    arc=0pt,
    boxrule=0pt,
    colback=white,
    top=3em, % you can change the top spacing
    overlay unbroken and first={
        % draw box on the left
        \node[fill=greentitleback,
            font=\color{greentitle}\sffamily\bfseries\large,
            anchor=south west,
            xshift=2mm,
            yshift=-2em, % you can change xshift and yshift to adjust the title placement
        ] (titlebox) at (frame.north west) 
        % notice the difference here, kaocounter is used instead
        {Exercise \refstepcounter{kaocounter}\thekaocounter
        % add cross-referencing support
        \IfValueT{#2}{\label{#2}}
        };

        % write title on the right
        \node[font=\color{drakgreentitle}\sffamily\large, 
        anchor=west
        ] at ($(titlebox.east)+(2mm,0mm)$) {#1};

        % draw the vertical line on the left
        \draw[draw=greentitleback, line width=2pt] 
            (titlebox.north west-|frame.north west)--(frame.south west);
    },
    overlay middle and last={
        \draw[draw=greentitleback, line width=2pt] 
            (frame.north west)--(frame.south west);
    }
    fonttitle=\color{greentitle}\sffamily\bfseries,
}

\DeclareTColorBox{genericbox}{m}{
    enhanced,
    breakable,
    arc=0pt,
    boxrule=0pt,
    colback=white,
    attach boxed title to top left,
    boxed title style={
        colback=white,
        colframe=white,
    },
    title={#1},
    fonttitle=\color{greentitle}\sffamily\bfseries\large
}

\begin{document}

\section{First Section}

\begin{bookexample}[My Title]
\Blindtext[4]
\end{bookexample}

\begin{genericbox}{Solution}
\Blindtext[2]
\end{genericbox}

\section{Second Section}

% an example with label
\begin{bookexample}[Another Title][ex:one]
\Blindtext[4]
\end{bookexample}

\begin{genericbox}{Solution}
\Blindtext[2]
\end{genericbox}

\textbf{I want to refer to Exercise \ref{ex:one}}.

% No title
\begin{bookexample}
\Blindtext[1]
\end{bookexample}

% No title, but has label
\begin{bookexample}[][ex:two]
\Blindtext[1]
\end{bookexample}

\textbf{I want to refer to Exercise \ref{ex:two}}.

\end{document}