\documentclass{article}
\usepackage{xcolor}
\usepackage{framed}
\usepackage{amsthm}
\newtheorem{thm}{Theorem}
\begin{document}
\section{Basics}

\begin{framed}
This is stuff that's framed.
\end{framed}

Note that the \begin{framed}framed\end{framed} stuff is a block!

\begin{framed}
This is stuff that's framed.

And it can hold multiple paragraphs.
\end{framed}

\begin{framed}
And even stuff in multiple Paragraphs.

\paragraph{Does this work?} But not in LaTeXML!
\end{framed}

\section{Variants}
\begin{oframed}
This is stuff that's framed, but would stay open at page breaks.
This doesn't make so much sense for LaTeXML, so it's pretty much
the same.
\end{oframed}

\definecolor{shadecolor}{rgb}{0.5,0.75,0.5}
\begin{shaded}
This is stuff that's shaded green;
should fade into the margin, whatever that means.
\end{shaded}

\begin{shaded*}
This is stuff that's shaded green;
it should end sharply at the margin.
\end{shaded*}

\begin{snugshade}
This is stuff that's snugly shaded green;
fading into the margin.
\end{snugshade}

\begin{snugshade*}
This is stuff that's snugly shaded green;
ending sharply at the margin.
\end{snugshade*}

\begin{leftbar}
This is with a left bar, like a changebar?
\end{leftbar}

\definecolor{TFFrameColor}{rgb}{0.5,0.5,0.75}
\definecolor{TFTitleColor}{rgb}{1,1,1}
\begin{titled-frame}{A Titled Frame}
This is a titled frame.
\end{titled-frame}

\begin{framed}
Lorem ipsum.
\begin{thm}
  A theorem.
\end{thm}
\end{framed}

\begin{shaded}
\begin{thm}
Para 1.
 
Para 2.
 

Para 3.
 
 
 
Para 4.
\end{thm}\end{shaded}

\end{document}