documentclass{scrbook}
usepackage[papersize={170mm,240mm}
            ,top=25mm
            ,inner=20mm
            ,outer=25mm
            ,marginparwidth=50pt
            ]{geometry}
usepackage[framemethod=tikz]{mdframed}
            mdfsetup{skipabove=2baselineskip,skipbelow=2baselineskip,frametitlefont=sffamilybfseriesLarge, needspace=4baselineskip, splittopskip=1.5baselineskip}
            mdfsetup{apptotikzsetting={tikzset{mdfbackground/.append style={draw=none}}}}
            mdfdefinestyle{greyexercise}{%
            everyline=true,ignorelastdescenders=true,
            linewidth=0pt,backgroundcolor=black!20,
            innerleftmargin=5mm, innerrightmargin=5mm, innerbottommargin=5mm, innertopmargin=5mm,
            frametitleaboveskip=15mm, frametitlebelowskip=5mm,frametitlerule=false, repeatframetitle=false,
            firstextra={useasboundingbox (P) rectangle (P);node[xshift=5mm,right,draw=black!20, line width=1.5pt,rectangle, minimum size=10mm, fill=white] at (P-|O) {color{black!20}%includegraphics[width=10mm]{.pdf}
                };},
            singleextra={useasboundingbox (P) rectangle (P);node[xshift=5mm,right,draw=black!20, line width=1.5pt,rectangle, minimum size=10mm, fill=white] at (P-|O) {color{black!20}%includegraphics[width=10mm]{.pdf}
                };}
            }
usepackage{lipsum,xcolor}

begin{document}

chapter{Witchcraft in Transylvania}
section{Origins 1840--1843}
lipsum[1-7]
begin{mdframed}[style=greyexercise,frametitle=Exercises]
        lipsum[1]
end{mdframed}
end{document}