Theorems spanning pages without losing width

Question

I use declaretheoremstyle to declare a theorem environment. I like the format of shaded, it gives a special background color without shorten the width of a text. But one problem is that a theorem block does not span in 2 pages. So if a block is too long, it intersects with the bottom margin of the page:

\documentclass{article}
\usepackage[english]{babel}
\usepackage[margin=2cm]{geometry}% just for the example
\usepackage{xcolor}
\usepackage{amsthm}
\usepackage{thmtools}
\usepackage{mdframed}

\declaretheoremstyle[
spaceabove=6pt, spacebelow=6pt,
headfont=\normalfont\bfseries,
postheadspace=1em,
notefont=\bfseries,
notebraces={(}{)},
bodyfont=\itshape,
shaded={bgcolor=yellow!20}
]{thmstyle}

\declaretheorem[style=thmstyle,name=Theorem]{theorem}

\begin{document}

\begin{theorem}[name]
...
\end{theorem}

\renewcommand{\listtheoremname}{List of Theorems}
\addcontentsline{toc}{section}{\listtheoremname}
\listoftheorems[ignoreall,show=theorem]

\end{document}

I tried to follow this proposition by using preheadhook and postfoothook. It does solve the problem of spanning, but it shortens the width of a text, as I showed here.

I think i will go with the authentic width (as shaded gives), does anyone know how to make it span in 2 pages?

Answer 1

Use the mdframed key to interact with the mdframed package and set the margins to the appropriate values (the settings I used in the code below reproduce the original settings):

\documentclass{article}
\usepackage[english]{babel}
\usepackage[margin=2cm]{geometry}% just for the example
\usepackage{xcolor}
\usepackage{amsthm}
\usepackage{thmtools}
\usepackage{mdframed}
\usepackage{lipsum}

\declaretheoremstyle[
headfont=\normalfont\bfseries,
postheadspace=1em,
notefont=\bfseries,
notebraces={(}{)},
bodyfont=\itshape,
mdframed={
  hidealllines=true,
  skipabove=10pt,
  backgroundcolor=yellow!20,
  innerrightmargin=2pt,
  innerleftmargin=2pt,
  innertopmargin=0pt,
  innerbottommargin=0pt,
  leftmargin=-2pt,
  rightmargin=-2pt,
  }
]{thmstyle}

\declaretheorem[style=thmstyle,name=Theorem]{theorem}
\renewcommand{\listtheoremname}{List of Theorems}

\begin{document}

\lipsum[4]
\begin{theorem}[Some name]
\lipsum[4]
\end{theorem}
\lipsum[4]

\end{document}

The output:

Answer 2

Here is a simple solution with the framed option of ntheorem, which has tools for selectively typeset theorem lists:

\documentclass{article}
\usepackage[english]{babel}
\usepackage[margin=2cm]{geometry}% just for the example
\usepackage[x11names]{xcolor}
\usepackage{lipsum}
\usepackage{amsmath}
\usepackage[thmmarks, thref, amsmath, framed]{ntheorem}
\usepackage{thmtools}

\usepackage{framed}
\colorlet{framecolor}{VioletRed4}
\theoremframepreskip{6pt}
\theoremframepostskip{6pt}
\theoreminframepreskip{4pt}
\theoreminframepostskip{4pt}
\theoremheaderfont{\upshape\bfseries}
\theorembodyfont{\itshape}
\theoremseparator{.}
\colorlet{shadecolor}{yellow!20}
\def\theoremframecommand{\colorbox{shadecolor}}
\newshadedtheorem{theorem}{Theorem}


\def\theoremframecommand{\setlength\fboxrule{1pt}\colorlet{shadecolor}{LavenderBlush2!60!}\fcolorbox{framecolor}{shadecolor}}
\theoremheaderfont{\scshape}
\theorembodyfont{\upshape}
\newshadedtheorem{defi}{Definition}

\theoremlisttype{allname}
\begin{document}
\vspace*{18cm}

Blahblahblah
\begin{theorem}[Named theorem]
  Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text.Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text.Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text.Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text.Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text.Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text. Some text.

  \lipsum[1]
\end{theorem}
Blah blah blah
\colorlet{shadecolor}{LavenderBlush2}
\begin{defi}
  $ \boldsymbol \pi $ is the ratio of the perimeter of a circle to its diameter.
\end{defi}
%
%\renewcommand{\listtheoremname}{List of Theorems}
%\listoftheorems[ignoreall,show=theorem]
\section*{\listtheoremname}
\addcontentsline{toc}{section}{\listtheoremname}
\listtheorems{theorem,defi}

\end{document}