documentclass{article}
usepackage[tikz]{mdframed}
usepackage{lipsum}
definecolor{greentitle}{cmyk}{.3,.02,.4,0}
makeatletter
newenvironment{understanding}[1][]%
  {begin{mdframed}[
   bottomline=false,
   leftline=false,
   linecolor=greentitle,
   backgroundcolor=white,
   roundcorner=0pt,
   linewidth=1pt,
   innerrightmargin=25pt,
   singleextra={
     fill[greentitle] (P) rectangle ([xshift=-13pt]P|-O);
     node[overlay,anchor=south east,rotate=90,font=color{white}scshape] at (P) {fontsize{10}    {12}selectfont{UNDERSTANDING}};
    },
  ]
 }
 {end{mdframed}}
makeatother
begin{document}
begin{understanding}
lipsum[2-3]
end{understanding}
end{document}