I prefer using tcolorbox
thinking that in future you may want the background to be fashionable. I have given many options (which are not needed for this particular case) in the tcbset
so that you can play with them to suit your needs.
\documentclass{article}
\usepackage[most]{tcolorbox}
\tcbset{
frame code={},
center title,
left=0pt,
right=0pt,
top=0pt,
bottom=0pt,
colback=gray!70,
colframe=white,
width=\dimexpr\textwidth\relax,
enlarge left by=0mm,
boxsep=5pt,
arc=0pt,outer arc=0pt,
}
\begin{document}
\begin{tcolorbox}
\textsc{Extra Curricular Achievements}
\end{tcolorbox}
\end{document}
Here is another option using framed
package.
\documentclass{article}
\usepackage{xcolor}
\usepackage{framed}
\definecolor{shadecolor}{RGB}{180,180,180}
\begin{document}
\begin{snugshade*}
\noindent\textsc{Extra Curricular Achievements}
\end{snugshade*}
\end{document}
Without extra packages:
\documentclass{article}
\usepackage{xcolor}
\definecolor{shadecolor}{RGB}{150,150,150}
\begin{document}
\noindent\colorbox{shadecolor}
{\parbox{\dimexpr\textwidth-2\fboxsep\relax}{\textsc{Extra Curricular Achievements}}}
\end{document}
And convert it in to a macro:
\documentclass{article}
\usepackage{xcolor}
\definecolor{shadecolor}{RGB}{150,150,150}
\newcommand{\mybox}[1]{\par\noindent\colorbox{shadecolor}
{\parbox{\dimexpr\textwidth-2\fboxsep\relax}{#1}}}
\begin{document}
\mybox{\textsc{Extra Curricular Achievements}}
\end{document}