\documentclass[main]{subfiles}
\begin{document}

%@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
% summarizes lecture 
% author:

\section{Algorithm Template}
\renewcommand{\arraystretch}{1.5}
\definecolor{lgray}{gray}{0.95}
\definecolor{gray}{gray}{0.9}

\rowcolors{1}{lgray}{gray}

Some introduction text.

\scriptsize
\todo[inline]{Add numbering lines at the left.}
\begin{verbatim}
things
     that happen,
           happen.
\end{verbatim}


\end{document}