changing formatting for section headers

Question

I would like my document to have section headings that look like this:

How can I achieve this in LaTeX?

Answer 1

For your final solution define the dark red color as desired and replace it with 'red' in my proposal. Note that in the below example the given design is also apllied to the section format.

The Code

\documentclass[11pt]{article}
\usepackage{lipsum}
\usepackage{xcolor}
\usepackage{titlesec}
  \titleformat{\section}
  {\normalfont\Large\itshape\color{red}}{%
    \hspace*{-4.5em}\rule[-1.35mm]{4.5em}{1.25em}
    {\color{white}\hspace{-1cm}\normalfont\thesection\hspace{5pt}}
  }{1em}{}
  \titleformat{\subsection}
  {\normalfont\large\itshape\color{red}}{%
    \hspace*{-4.5em}\rule[-1.35mm]{4.5em}{1.25em}
    {\color{white}\hspace{-1cm}\normalfont\thesubsection\hspace{5pt}}
  }{1em}{}

\begin{document}
\section{Introduction}
\lipsum[1]
\subsection{Laplace Transformation}
\lipsum[2-4]
\end{document}

Output