# Box in a theorem environment

I am solving some exercises for my master program. I am including question and answer in a theorem environment. I would also like to have the question inside a gray box. The thing is that the gray box isn't placed well, as indicated in the following figure.

What I would like to have, concerning the gray box, the second line within gray box to start bellow Exercise 1. My code is

\documentclass[a4paper,11pt]{article}
\usepackage{kerkis}
\usepackage{amsmath}
\usepackage{xcolor}
\newcommand*{\mybox}[2]{\colorbox{#1!30}{\parbox{.98\linewidth}{#2}}}
\newtheorem{exe}{Exercise}
\begin{document}
\begin{exe}\mybox{gray}{Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla Bla bla bla }
\end{exe}
\end{document}


Any ideas on that?

-
I suppose that \parbox[t]{.98\linewidth} might do better. –  egreg Dec 9 '12 at 10:48
@egreg: Thank you very much for your answer! Perhaps I didn't described it well. I would like the second line to begin under Exercise 1. –  Thanos Dec 9 '12 at 11:05

Here's one possible solution such that the environment even admits page breaks (feel free to make the adjustments that best suit your needs):

\documentclass{article}
\usepackage{amsthm}
\usepackage{xcolor}
\usepackage{mdframed}
\usepackage{thmtools}
\usepackage{lipsum}

\declaretheoremstyle[
backgroundcolor=gray!60,
hidealllines=true,
innertopmargin=0pt,
skipabove=\topsep,skipbelow=\topsep]},
prefoothook=\end{mdframed}
]{mystyle}
\declaretheorem[style=mystyle,name=Exercise]{exe}

\begin{document}

\lipsum[4]
\begin{exe}
\lipsum[4]
\end{exe}
\lipsum[4]

\end{document}


-
That was exactly what I wanted to do!!! Thank you so much! –  Thanos Dec 9 '12 at 13:08
I was trying to make an example just to show how bad it appears. ;-) –  egreg Dec 9 '12 at 13:13
@egreg: You really think so? What do you think is the best? The thing is that I want to highlight somehow the question, and give the solution bellow... –  Thanos Dec 9 '12 at 13:15

Is this what you have in mind?

\documentclass[a4paper,11pt]{article}
\usepackage{kerkis}
\usepackage{amsmath}
\usepackage{xcolor}
\usepackage{lipsum} % for mock text

\newtheorem{exeX}{Exercise}
\newsavebox{\exebox}
\newenvironment{exe}[1]
{\newcommand{\execolor}{#1}%
\begin{exeX}\mbox{}\\*[3pt]
\begin{lrbox}{\exebox}
\begin{minipage}{\dimexpr\linewidth-2\fboxsep\relax}}
{\end{minipage}\end{lrbox}\colorbox{\execolor}{\usebox{\exebox}}\end{exeX}}

\begin{document}

\begin{exe}{red}
\lipsum*[2]
\end{exe}

\end{document}


The minipage and the inner theorem environment, together with lrbox avoid the need of stating \mybox inside the exe environment; the color should be specified as the argument to exe.

Note that the minipage width is computed so that it fills correctly the line width.

-
Thank you so much for your answer! Actully I would like the first line to be next to Exercise 1 and the second line to begin bellow E in Exercise 1. –  Thanos Dec 9 '12 at 11:25
@Thanos Should Exercise 1 be on the same colored background? –  egreg Dec 9 '12 at 11:27
No. That is exactly what I was trying to achieve... –  Thanos Dec 9 '12 at 11:31