TikZ Tcolorbox – How to Write Exercises in A Specific Style?

Question

I am trying to write to code that makes exercices look like the picture below. Here’s my code. The stars give information about the exercice difficulty level which are graded 1,2 or 3. The first is picture i want and the second, what i actually have Thanks for any help

\documentclass[11pt]{book}
\usepackage[margin=2.5cm]{geometry}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{lmodern}
\usepackage{mathrsfs}

\usepackage{amsmath,amssymb}
\usepackage[most]{tcolorbox}
\newtcolorbox{exercisebox}%
    {
    enhanced,
    breakable,
    colback=white, colframe=green!15!white,
    colbacktitle=white!15!pink, coltitle=pink!50!black,
    left=0pt,right=0mm,top=3mm,bottom=3mm,
    pad at break=0pt,bottomrule at break=0pt,toprule at break=0pt,
    borderline={0mm}{0mm}{green!50!white,dashed},
    attach boxed title to top center={yshift=-2mm},
    boxed title style={boxrule=0.4pt},
    title=EXERCICES,
    }

\usepackage{eso-pic}
\usepackage{etoolbox}
\usepackage{enumitem}
\newcommand\circitem[1]{%
    \tikz[baseline=(char.base)]{%https://tex.stackexchange.com/questions/204116/uniform-size-of-circles-around-enumitems
        \node[circle,draw=gray, fill=gray!30,
              minimum size=1.2em,inner sep=0] (char) {#1};}}
\newcommand\boxitem[1]{%
    \tikz[baseline=(char.base)]{%https://tex.stackexchange.com/questions/204116/uniform-size-of-circles-around-enumitems
        \node[fill=orange!30,
              minimum size=1.2em,inner sep=0] (char) {#1};}}
\AtBeginEnvironment{tcolorbox}{%
    \setlist[enumerate,1]{label=\protect\boxitem{\arabic*}}
    \setlist[enumerate,2]{label=\protect\circitem{\alph*}}
                          }
\usepackage{fancyhdr}
\usepackage{cancel}
\usepackage{xcolor}
\newcommand\Exercice[1]{\fboxrule1.5pt%
\fcolorbox{gray}% frame
          {cyan}% background
          {\large\itshape\textbf{Exercise~#1}}%
          \par\medskip}

\usepackage{graphicx}
\usepackage{pgfplots}
\pgfplotsset{compat=1.16}
\usetikzlibrary{arrows}
\usepackage{tkz-tab}
\usepackage{mdframed}

\usepackage{varwidth}
\usepackage{listings}
\usepackage{pstricks-add}
\usepackage{hyperref}


\usepackage{lipsum}

\begin{document}
\section{EXERCICES}

\begin{exercisebox}
\Exercice{1}
Determiner la valeur de $a$ pour que $f$ définie par:\\
$\begin{cases}
f(x)=\dfrac{\sqrt{\sin(x)}-1}{x-\frac\pi2};\text{ si } x\ne\frac\pi2\\
f\left(\dfrac\pi2\right)=a
\end{cases}$ soit continue en $\dfrac\pi2$


\end{exercisebox}
\end{document}

Answer 1

\documentclass{article}

\usepackage{amsmath,amssymb}
\usepackage{nccmath}

\usepackage{tcolorbox}
\tcbuselibrary{skins}
\usetikzlibrary{decorations.pathmorphing, positioning}

\newcounter{mycounter}
\setlength{\parindent}{0pt}
\definecolor{myblue}{RGB}{0,163,217}

\usepackage{fontawesome}
\newcommand{\onestar}{\faStar~\faStarO~\faStarO}                                     % difficulty ratings. I you don't want the outlined but empty star, remove \faStarO.
\newcommand{\twostar}{\faStar~\faStar~\faStarO}
\newcommand{\threestar}{\faStar~\faStar~\faStar}

\usepackage{lipsum}                                                                  % for dummy text in the example boxes.
\begin{document}

\newtcolorbox{mybox}[1][\onestar]{                                                   % \onestar is the default difficulty.
    step=mycounter,                                                                  % boxes are automatically numbered    
    enhanced,
    colback=white,                                                                   % white background
    frame hidden,                                                                    % hide frame
    top=10pt, left=0pt, right=0pt,                                                   % top, left and right distances to the invisible borders of the box
    borderline north={1pt}{0pt}{green!75!black,                                      % green zig zag line
                                decoration={zigzag,
                                            amplitude=2pt,
                                            pre=moveto,pre length=4.25cm, 
                                            post length=6.75cm},
                                decorate},
    overlay={%
        \tikzset{overlay=false, draw=none, anchor=west}
        \node[fill=myblue, text=red,                                                 % background and textcolor of "Exercise" box
              minimum height=1.5em] at (frame.north west) (box1){\textbf{Exercise}}; % position of "Exercise" box
        \node[fill=myblue, text=red,                                                 % background and textcolor of exercise number box
              right = 1mm of box1,                                                   % position of exercise number box
              minimum height=1.5em] (box2){\textbf{\themycounter}}; 
        \node[text=orange, fill=white,                                               % background and textcolor of difficulty rating box
              right = 3mm of box2, ] (difficulty){#1};                               % position of difficulty rating box
    }}

\begin{mybox}[\onestar]
Simplifier les expressions suivantes:
\begin{enumerate}
    \item $A=\mfrac{5^3\times(3^2\times2)^{-1}}{3^{-1}\times(2^{-3}\times5)^2}$
    \item ...
\end{enumerate}
\end{mybox}

\begin{mybox}[\twostar]
\lipsum[1][1-3]
\begin{enumerate}
    \item \lipsum[1][1-1]
    \item ...
\end{enumerate}
\end{mybox}

\begin{mybox}[\threestar]
\lipsum[1][1-3]
\begin{enumerate}
    \item \lipsum[1][1-1]
    \item ...
\end{enumerate}
\end{mybox}

\begin{mybox}
\lipsum[1][1-3]
\begin{enumerate}
    \item \lipsum[1][1-1]
    \item ...
\end{enumerate}
\end{mybox}



\end{document}