SUpO9用tcolorbox制作的样式代码:

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

\definecolor{greentitle}{RGB}{61,170,61}
\definecolor{greentitleback}{RGB}{216,233,213}

\newtcolorbox[
  auto counter,
  number within=section
]{myexample}[2][]{%
  breakable,
  enhanced,
  colback=white,
  colbacktitle=white,
  arc=0pt,
  leftrule=1pt,
  rightrule=0pt,
  toprule=0pt,
  bottomrule=0pt,
  titlerule=0pt,
  colframe=greentitleback,
  fonttitle=\normalcolor,
  overlay={
    \node[
      outer sep=0pt,
      anchor=east,
      text width=2.5cm,
      minimum height=4ex,
      fill=greentitleback,
      font=\color{greentitle}\sffamily\scshape
    ] at (title.west) {example~\thetcbcounter};
  },
  title=#2,
  #1
}
\newcommand\Solution{\par\textbf{\textsf{Solution}}\par\medskip}

\begin{document}

\section{A test section}
\begin{myexample}{Factorise $x^2-2x+1$}
\Solution
 \lipsum[4]
\end{myexample}

\end{document}

用mdframed包制作的代码如下:

\documentclass{article}
\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}}
\newcommand\Solution{\par\textbf{\textsf{Solution}}\par\medskip}

\begin{document}

\section{A test section}
\begin{myexample}{Factorise $x^2-2x+1$}
\Solution
 \lipsum[4]
\end{myexample}

\end{document}

选自:http://tex.stackexchange.com/questions/212943/fancy-example-environment