% !TEX encoding = ITF-8 Unicode
\documentclass[12pt,a4paper]{book}
\usepackage{amsthm,amssymb,amsmath}
\usepackage{graphicx}
\usepackage{tikz} 
\usetikzlibrary{arrows,decorations.pathmorphing,backgrounds,positioning,fit,petri}
\usetikzlibrary{calc,intersections,through,backgrounds}
\usetikzlibrary{chains}
\usepackage[europeanresistors,americaninductors]{circuitikz}
\usetikzlibrary{automata,positioning}
\usepgflibrary{shapes.arrows}
\usetikzlibrary{shapes.arrows}
\usepgflibrary{shapes.misc}
\usetikzlibrary{shapes.misc}
%\usepackage{fancyhdr}

\def\thesection{\arabic{section}.\thechapter}

\usepackage[top=5cm, right=4cm, bottom=5cm, left=3.5cm]{geometry}
\usepackage{fancyhdr}
\pagestyle{fancy}
%\renewcommand{\sectionmark}[1]{\markright{#1}}
\renewcommand{\rightmark}{\thesection}
%\renewcommand{\sectionmark}[1]{\rightmark{\thechapter{.}\thesection.\ #1}}
\addtolength{\headwidth}{0pt} 
\addtolength{\headwidth}{0pt}
\fancyhf{}
\fancyhead[LO]{\small{\rightmark}}
\fancyhead[RO]{\thepage}
\fancyhead[RE]{\small\nouppercase{\leftmark}}
\fancyhead[LE]{\thepage}
\renewcommand{\headrulewidth}{0pt} 
\renewcommand{\footrulewidth}{0pt}
\usepackage{xepersian}
\settextfont[Scale=1]{Yas}
\setdigitfont[Scale=1]{PGaramond}
\setlatintextfont[ExternalLocation,BoldFont={lmroman10-bold},BoldItalicFont={lmroman10-bolditalic},ItalicFont={lmroman10-italic}]{lmroman10-regular}
\defpersianfont\nastaliq[Scale=2]{IranNastaliq}
\defpersianfont\titr[Scale=1]{B Titr}
\defpersianfont\traffic[Scale=1]{B Traffic}

\renewcommand\section[1]{\vskip 5pt \par\noindent\refstepcounter{section}{\textbf{\hboxR{\begin{tikzpicture}[node distance=0cm]
\setRTL
\node  [rectangle, fill=gray!30, text=black, minimum width=0.5cm,minimum height=0.5cm,align=center] (box5) {
    \begin{minipage}[t!]{0.03\textwidth}
       \thesection
    \end{minipage}
    };
   \node [rectangle, text=blue,minimum width=1cm,left = of box5, font=\fontsize{16}{16}\selectfont] (box1){\begin{minipage}[t!]{0.8\textwidth}
        #1 
    \end{minipage}};
\end{tikzpicture}}}}\\}
\begin{document}

\chapter{??? ???}
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\section{??? ???}
\newpage
shahlla shahlla
\newpage
shahlla shahlla
\end{document}