I want to increase the font width(size) for all document by package{lmodern},

Question

\documentclass[12pt]{book}
\usepackage{lmodern}
\usepackage{eulervm}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{mathrsfs}
\usepackage{amsthm}
\usepackage{mathtools}
\usepackage{hyperref}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[french]{babel}
\usepackage[top=2cm, bottom=2cm, left=2cm, right=2cm]{geometry}
\usepackage{enumitem}
\usepackage{csquotes}
\usepackage[x11names]{xcolor}
\usepackage{framed, etoolbox}
\colorlet{framecolor}{VioletRed4}
\colorlet{shadecolor}{LavenderBlush2!60}
\usepackage{thmtools} %
\usepackage{sectsty}
\chapterfont{\color{Firebrick2}}  % sets colour of chapters
\sectionfont{\color{Chartreuse4}}
\subsectionfont{\color{blue}}
%talwin majzo2at
%\usepackage{sectsty}%
%\chapterfont{\color{Firebrick2}}
%\usepackage{titlesec}%%%%%% <---------addendum
%\titleformat{\section}%%%%%% <---------addendum
%{\color{Chartreuse4}\normalfont\Large\bfseries}%%%%%% <---------addendum
%{\color{Chartreuse4}\thesection}{1.5em}{}%%%%%% <---------addendum
%\titleformat{\subsection}%%%%%% <---------addendum
%{\color{Firebrick3}\normalfont\Large\bfseries}%%%%%% <---------addendum
%{\color{Firebrick3}\thesection}{1.5em}{}%%%%%% <---------addendum


\makeatletter
\define@key{thmdef}{frame}[{}]{%
 \thmt@trytwice{}{%
 \RequirePackage{framed}%
 \RequirePackage{thm-patch}%
    \def\FrameCommand{\fcolorbox{framecolor}{shadecolor}}
 \addtotheorempreheadhook[\thmt@envname]{%
 \begin{framed}}%
 \addtotheorempostfoothook[\thmt@envname]{\end{framed}}%
 }%
}
\makeatother




\usepackage{thmtools}
\declaretheoremstyle[
    spaceabove=-6pt, 
    spacebelow=6pt, 
    headfont=\normalfont\bfseries, 
    bodyfont = \normalfont,
    postheadspace=1em, 
    qed=$\blacksquare$, 
    headpunct={:}]{myproofstyle} %<---- change this name
\declaretheorem[name={Proof}, style=myproofstyle, unnumbered]{Proof}

\declaretheoremstyle[
    spaceabove=6pt, 
    spacebelow=6pt, 
    headfont=\bfseries,
    notefont=\bfseries, 
    notebraces={(}{)}, 
    bodyfont=\itshape,
    postheadspace=1em,
    headpunct={:}]{mystyle}

    \declaretheoremstyle[
    spaceabove=6pt, 
    spacebelow=6pt, 
    headfont=\normalfont\bfseries,
    notefont=\mdseries\bfseries, 
    notebraces={({)}}, 
    bodyfont=\normalfont,
    postheadspace=1em,
    postheadhook = {\hspace{0mm}\newline},%
    headpunct={:},]{myst}

\declaretheorem[name={Théorème}, style=mystyle,numberwithin=section]{thm}
\declaretheorem[frame,name={Lemme}, style=mystyle,numberwithin=section]{lema}
\declaretheorem[frame,name={Définition}, style=mystyle,numberwithin=section]{defi}
\declaretheorem[frame,name={Corollaire}, style=mystyle,numberwithin=section]{coro}
\declaretheorem[frame,name={Proposition}, style=mystyle,numberwithin=section]{props}
\declaretheorem[frame,name={Vocabulaire}, style=mystyle,numberwithin=section]{voc}
\declaretheorem[name={Preuve}, style=myst,numbered=no]{preuve}
\declaretheorem[name={Remarque}, style=myst,numberwithin=section]{remark}
\declaretheorem[name={Remarques}, style=myst,numberwithin=section]{remarks}
\declaretheorem[name={Exemple}, style=myst,numberwithin=section]{exemple}
\declaretheorem[name={Exemples}, style=myst,numbered=no]{exemples}
\declaretheorem[name={Méthode}, style=mystyle,numberwithin=section]{methode}
\declaretheorem[name={Méthodes}, style=mystyle,numbered=no]{methodes}
\declaretheorem[name={Notation}, style=mystyle,numbered=no]{notation}






\AtBeginEnvironment{defi}{\colorlet{framecolor}{black}
    \colorlet{shadecolor}{orange!15}}
\newcommand{\myarrow}[1][1cm]{\mathrel{%
   \hbox{\rule[\dimexpr\fontdimen22\textfont2-.2pt\relax]{#1}{.4pt}}%
   \mkern-4mu\hbox{\usefont{U}{lasy}{m}{n}\symbol{41}}}}
   \AtBeginEnvironment{voc}{\colorlet{framecolor}{black}
    \colorlet{shadecolor}{LightSkyBlue2!25}}
    \AtBeginEnvironment{props}{\colorlet{framecolor}{black}
    \colorlet{shadecolor}{Yellow1!15}}
     \AtBeginEnvironment{coro}{\colorlet{framecolor}{black}
    \colorlet{shadecolor}{Yellow1!15}}
    \AtBeginEnvironment{lema}{\colorlet{framecolor}{black}
    \colorlet{shadecolor}{Yellow1!15}}

\makeatletter

\setbox0\hbox{$\xdef\scriptratio{\strip@pt\dimexpr
    \numexpr(\sf@size*65536)/\f@size sp}$}

\newcommand{\myscriptarrow}[1][1cm]{{%
    \hbox{\rule[\scriptratio\dimexpr\fontdimen22\textfont2-.2pt\relax]
               {\scriptratio\dimexpr#1\relax}{\scriptratio\dimexpr.4pt\relax}}%
   \mkern-4mu\hbox{\let\f@size\sf@size\usefont{U}{lasy}{m}{n}\symbol{41}}}}

\makeatother
\newcommand*{\QED}{\hfill\ensuremath{\blacksquare}}%Heron

\usepackage{amsmath,amscd}
\usepackage{mathtools}

\usepackage{dsfont}


\usepackage{enumitem}

\usepackage{textcomp}

\usepackage{tikz, tikz-cd}
\usepackage{amssymb}

\newlength{\leftbarwidth}
\newlength{\leftbarsep}
\newcommand*{\leftbarcolorcmd}{\color{leftbarcolor}}
\renewenvironment{leftbar}{
\def\FrameCommand{{\leftbarcolorcmd{
\vrule width \leftbarwidth \hspace{\leftbarsep}}}
\fboxsep=\FrameSep\colorbox{colorboxcolor}
}
\MakeFramed {\advance \hsize-\width \FrameRestore}
}{
\endMakeFramed}

\begin{document}
{\fontsize{68}{68} \selectfont Text}
deux sous-groupes
\chapter{Notion d'extension de corps }
\section{Extension d'anneau}
\begin{defi}
deux sous-groupes
Soit $A$ un anneau, on appel \textbf{\textcolor{blue}{extension}}  de $A$ tout anneau $B$
tel que $A$ est une sous-anneau de $B$. Dans ce cas on note \textcolor{blue}{$B/A$} ou \textcolor{blue}{$B:A$} ou \textcolor{blue}{$A\myarrow B$}.
\end{defi}
\section{Extension de corps}
Maintenant on introduisant la notion d'extension de corps.
\begin{defi}
Étant donné un corps $K$, on appelle \textbf{\textcolor{blue}{extension}} de $K$ tout corps $L$ contenant $K$ et on note  \textcolor{blue}{$L/K$} ou \textcolor{blue}{$L:K$} ou \textcolor{blue}{$K\myarrow L$}.
\end{defi}
\begin{exemples}
\newlist{coloritemize}{itemize}{1}
\setlist[coloritemize]{label=\textcolor{blue}{\textbullet}}
\begin{coloritemize}
  \item Tout corps de caractéristique $0$ est une extension du corps $\mathds{Q}$.
   En particulier, les inclusions $\mathds{Q} \subset \mathds{R}\subset \mathds{C}$ montrent que $\mathds{R}$ et $\mathds{C}$ sont extensions de $\mathds{Q}$ et que $\mathds{C}$ est extension de $\mathds{R}$.\\
 Utilisons les notations donc on a : $\mathds{C}/\mathds{R}$,   $\ \mathds{C}/\mathds{Q}$,     $\ \mathds{R}/\mathds{Q}$.
 \item Soit $L:=\{p+qi\  |\  (p,q)\in \mathds{Q}\times \mathds{Q}\  et\  i^2=-1 \}$.\\
 On vérifie que $L$ est un sous-corps de $\mathds{C}$ contenant $\mathds{Q}$, donc L est une extension de $\mathds{Q}$, et, $\mathds{C}$ est une extension de $L$.
\end{coloritemize}
\end{exemples}

\end{document}

Answer 1

You could use the memoir class (a superset of the book class) which provides options for font sizes ranging from 9pt to 60pt