\documentclass[a4paper, 12pt, twoside]{report}

\usepackage[utf8x]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}

\usepackage{fixltx2e}
\usepackage{ellipsis}
\usepackage{ragged2e}
\usepackage[tracking=true]{microtype}

\usepackage[english]{babel}
\usepackage[left=3cm,right=3cm,top=3cm,bottom=3cm]{geometry}

\usepackage{marginnote}
\usepackage{graphicx}
\usepackage{xcolor}

\usepackage{tikz}
\usepackage{tikz-cd}


\usepackage{setspace}
\renewcommand{\baselinestretch}{1.1} 

\usepackage{todonotes}
% get rid of rounded corners in todonotes
\makeatletter
\tikzstyle{notestyleraw}=[
draw=\@todonotes@currentbordercolor,
fill=\@todonotes@currentbackgroundcolor,
line width=0.6pt,
text width=\@todonotes@textwidth-1.6ex-1pt,
inner sep=0.8ex
]
\makeatother
% todonotes setup
\colorlet{draftnotesbgcolor}{orange}
\presetkeys{todonotes}{linecolor=draftnotesbgcolor, backgroundcolor=draftnotesbgcolor, bordercolor=draftnotesbgcolor, figcolor=white}{}

\usepackage{lecture-notes}


% boolean value to indicate if WorkingOn, EditorNote and AdditionalInfo produce visible output
\newboolean{showAdditionalContent}
% \setboolean{showAdditionalContent}{false}
\setboolean{showAdditionalContent}{true}


% \titleformat{\chapter}{\normalfont\Large\filcenter}{\thechapter.\hspace*{0.2cm}}{0cm}{#1}

% Setup headlines
\usepackage[explicit]{titlesec}
\titleformat{\section}{\normalfont\Large\filcenter}{\thesection.\hspace*{0.2cm}}{0cm}{#1}
%\titleformat{name=\section,numberless}{\normalfont\Large\filcenter}{}{0cm}{#1}w
\titlespacing{\section}{0cm}{0.6cm}{0.4cm}

\titleformat{\subsection}{\normalfont\large\filcenter}{\thesubsection.\hspace*{0.2cm}}{0cm}{#1}
\titlespacing{\subsection}{0cm}{0.6cm}{0.4cm}

% Setup table of contents
\usepackage[titles]{tocloft}
%\cftsetindents{section}{0cm}{2cm}
%\renewcommand\cftsecpresnum{Lecture }
%\crefname{section}{Lecture}{Lectures}

\renewcommand\thesection{\arabic{section}} 
\renewcommand\thechapter{\Roman{chapter}} 


\begin{document}

% cover page
\input{frontmatter}

\input{contents}

\nocite{*}
\bibliographystyle{amsalpha}
\bibliography{literature}

\printindex

\end{document}