How to create a tcolorbox with fancy title box and with left and bottom borderlines

Question

I would like to use the tcolorbox below to hold exercises for my students. I tried to reproduce with codes below:

\documentclass[12pt,a4paper]{article} 
\usepackage{tcolorbox} 
\usepackage{amsmath,amssymb}
 \xdefinecolor{myblue}{RGB}{102, 53, 153} 
\tcbuselibrary{skins} 
\newtcolorbox[auto counter]{myfan}{% empty,
    sharp corners, enhanced, attach boxed title to top left, boxed title style={% empty, left=0pt, right=0pt, frame code ={\draw[line width=.5mm,myblue]([xshift=13mm]frame.north east)--([xshift=15mm]frame.east)-
    -([xshift=13mm]frame.south east);
    \draw[line width=.5mm,myblue]([xshift=14mm]frame.north east)-- ([xshift=16mm]frame.east)--([xshift=14mm]frame.south east); \draw[line width=.5mm,myblue]([xshift=10mm]frame.north east)-- ([xshift=12mm]frame.east)--([xshift=10mm]frame.south east); \draw[line width=.5mm,myblue]([xshift=11mm]frame.north east)-- ([xshift=13mm]frame.east)--([xshift=11mm]frame.south east); }
    }, 
underlay boxed title={%
    \draw[myblue] (title.south east) -- (title.north east)-- ([xshift=4.3ex]title.north east)--([xshift=4.3ex]title.south east)-- (title.south west);
    \path([xshift=2.25ex]title.east)node[inner sep=0pt,text=black]{{\LARGE\fontfamily{bch}\selectfont\thetcbcounter}};
    \fill[fill=myblue](title.south west)--(title.north west)--(title.north east)--(title.south east); },
    frame hidden,
    borderline west={1.5pt}{0pt}{myblue}, 
borderline south={1.5pt}{0pt}{myblue}, colback=white, coltitle=white, title={Exercise}, } 
\begin{document}
    \begin{myfan}
 \begin{enumerate} 
\item Competition at the workplace can be a double-edged sword. \item It definitely keeps us motivated to perform better and to achieve our goals.
    \item However, it can also lead to several negative consequences if not managed correctly. 
\end{enumerate} 
\end{myfan} 
\end{document}

Which gave me the image below:

Answer 1

Your question is not clear, but I think you want something like this:

\documentclass[12pt,a4paper]{article} 
\usepackage{tcolorbox} 
\usepackage{amsmath,amssymb}
\xdefinecolor{myblue}{RGB}{102, 53, 153} 
\tcbuselibrary{skins} 

\newtcolorbox[auto counter]{myfan}{% empty,
    sharp corners, enhanced, attach boxed title to top left, 
    boxed title style={% 
        empty, left=0pt, right=0pt, 
        frame code ={
            \foreach \i [evaluate=\i as \ni using \i+2,
                count=\xi from 0, evaluate=\xi as \op using 1-2*\xi/10] in {10,11,12,13}{ 
                \draw[line width=.5mm,myblue, opacity=\op]([xshift=\i mm]frame.north east)--([xshift=\ni mm]frame.east)
                --([xshift=\i mm]frame.south east);}
        }
    }, 
    underlay boxed title={%
        \path([xshift=2.25ex]title.east) node[inner sep=0pt,text=black, font=\Large\fontfamily{bch}] (number) {\thetcbcounter};
        \fill[fill=myblue](title.south west)--(title.north west)--(title.north east)--(title.south east); 
        \draw[myblue, rounded corners=1mm] ([yshift=-.5\pgflinewidth]title.north east) -| ([xshift=2mm]number.east) [sharp corners]|- (title.south west);
},
    frame hidden,
    borderline west={1.5pt}{0pt}{myblue}, 
    borderline south={1.5pt}{0pt}{myblue}, colback=white, coltitle=white, title={Exercise}, 
    overlay={\draw[line width=1.5pt, myblue] (frame.south east)--++(90:5mm);}
    } 

\begin{document}
\begin{myfan}
 \begin{enumerate} 
\item Competition at the workplace can be a double-edged sword. \item It definitely keeps us motivated to perform better and to achieve our goals.
    \item However, it can also lead to several negative consequences if not managed correctly. 
\end{enumerate} 
\end{myfan} 
\end{document}