Page Layout ⇒ Chapter and section style in latex thesis

[Raly]

I'm new in the latex community and actually I don't know if I'm posting my question in the right place
I would like to add a colored box around the chapter number and section number, I want to get the same style as the photo attached but I don't know how to do this. I appreciate if someone can help me.
I'm using texshop.

[Ijon Tichy]

This depends on the class you are using and if you are using a package for the chapter/section titles like titlesec also on that package. So without minimal working example I can only gamble and give some general information: With the standard classes book and report you need an extra package. See e.g. the already linked titlesec. With a KOMA-Script class you can change the chapter number format redefining \chapterformat, e.g., using \renewcommand*{\chapterformat}{\colorbox{red}{\textcolor{white}{\thechapter}}\enskip}. There are also commands for other section levels and \chapterlinesformat and \sectionlinesformat for advanced changes. See the manual and several examples in the internet for more information. memoir also has its own commands so configure the chapter title. See the manual for more information. Other classes may also have similar features (again, see the manual) or allow to use titlesec.

Note, a more detailed answer needs a lot of more information in the question, not only a minimal working example but, e.g., also information on how the formatting of chapter/section titles with more than one line can should be.

[Raly]

Thanks for your replay.
I prepared an example of what I'm using, I'm using the titlesec package
I attached an example file.

\documentclass[a4paper,11pt,twoside,english]{book}
\usepackage[a4paper,top=2.5cm,bottom=2.5cm,left=3cm,right=2.5cm]{geometry}
\linespread{1.3}

\usepackage{titlesec}
\usepackage[Glenn]{fncychap}

\begin{document}
\include{SM_new}
\end{document}

Now, I tried to use what you suggested

\renewcommand*{\chapterformat}{\colorbox{red}{\textcolor{white}{\thechapter}}\enskip}

but it give error that \chapterformat not defined.

should I include any package before using renew command ?

Thanks in advanced.