design a style using tikz package

Question

How can I use latex tikz package to design the style that is seen in the picture?

Answer 1

Here is a solution using titlesec , xcolor, colortbl, geometry and lettrine (this last one only for my pleasure…). I was unsure whether the light blue background was also required, so there's none in my code, but that can be changed:

    \documentclass[12pt]{book}
    \usepackage[utf8]{inputenc}
    \usepackage{microtype}
    \usepackage[garamond]{mathdesign}
    \usepackage{garamondx}%%
    \usepackage[x11names]{xcolor}
    \usepackage{tabularx, colortbl}

    \usepackage{geometry}
    \usepackage{titlesec}%
    \usepackage{lettrine}
    \renewcommand\LettrineFontHook{\fontfamily{EBGaramondInitials-TLF}\color{titlecolour}}

    \colorlet{titlecolour}{Cyan4!85!}
    \newlength\labelframewd
    \settowidth{\labelframewd}{\lsstyle\scshape\small\MakeLowercase{\chaptername}}

    \newsavebox\chaplabelbox%

    \newcommand\chaplabel{\color{titlecolour}%
    \begin{tabularx}{\linewidth}{c@{\enspace}X}
        \lsstyle\scshape\small\MakeLowercase{\chaptername}\\
        \cellcolor{titlecolour}\raisebox{-1ex}[5ex][20ex]{\color{black}\bfseries\fontsize{36}{40}\selectfont\thechapter} & \titlerule[3pt]
        \end{tabularx}
    }%

    \titleformat{\chapter}[display]{\centering}
    {\setlength{\tabcolsep}{0pt} \smash{\chaplabel}}%
    {2ex}
    {\thispagestyle{empty}\vskip-10ex\hskip\labelframewd\fontsize{28}{32}\selectfont\bfseries}%

    \titlespacing{\chapter}{0pt}{1.25\baselineskip}{10\baselineskip}
    \renewcommand*\thechapter{\arabic{chapter}}

    \begin{document}

    \chapter{Tweedledee \& Tweedledum}

    \lettrine{T}{ext} text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text.

    \end{document}