# Equations and Equation Numbers within a Box

I use the code below to make a box around equations. It puts the equations numbers outside the box, however I would like to have the equation numbers within the box.

How can I alter my code to do this? Thanks in advance.

\documentclass[11pt]{report}

\usepackage{empheq}

\newcommand*\widefbox[1]{\fbox{\hspace{2em}#1\hspace{2em}}}

\begin{document}
\begin{empheq}[box=\widefbox]{align}
& a = b +c \\
& d = e+f
\end{empheq}
\end{document}


(So: I would like to have the ''(1)'' and ''(2)'' within the box.)

For a change, use tcolorbox:

\documentclass[11pt]{report}

\usepackage[most]{tcolorbox}
\tcbset{myformula/.style={colback=white, %yellow!10!white,
colframe=black, %red!50!black,
top=0pt,bottom=0pt,left=0pt,right=0pt,
boxsep=0pt,
arc=0pt,
outer arc=0pt,
}}

\begin{document}
\begin{tcolorbox}[ams align,myformula]
& a = b +c \\
& d = e+f
\end{tcolorbox}
\end{document}


Before I know for tcolorbox I use the following solution:

\documentclass{article}
\usepackage{empheq}

\newlength\fsep
\setlength\fsep{2\fboxsep+2\fboxrule}
\newsavebox\widebox
\newenvironment{mathbox}
{\par\vskip\fsep\noindent%
\begin{lrbox}{\widebox}%
\begin{minipage}{\textwidth-\fsep}%
}{\vskip\fsep\end{minipage}\end{lrbox}
\framebox{\usebox\widebox}%
}

\begin{document}
\begin{mathbox}
\begin{align}
a & = b +c \\
d & = e+f
\end{align}
\end{mathbox}
\end{document}


which gives:

Here is a simple solution with the framed package. I define a myframedeq environment, which has one optional argument, the width of the frame (default: \textwidth). One could in the same way define a shadedeq environment which would put wrap the math environment is a coloured box, with a coloured background.

\documentclass[11pt]{report}
\usepackage[showframe]{geometry}
\usepackage{empheq}
\usepackage{xcolor, framed}

\newcommand*\widefbox[1]{\fbox{\hspace{2em}#1\hspace{2em}}}
\newenvironment{myframedeq}[1][\linewidth]{\FrameSep=4pt\abovedisplayskip=0pt\belowdisplayskip=0pt
\framed\hsize=#1\leftskip=\dimexpr(\textwidth-#1)/2\relax}
{\endframed}

\begin{document}
\begin{empheq}[box=\widefbox]{align}
& a = b +c \\
& d = e+f
\end{empheq}
Text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text
\begin{myframedeq}
\begin{align}
a & = b + c \\
d & =e + f
\end{align}
\end{myframedeq}

\FrameRule=1pt
\begin{myframedeq}[0.6\linewidth]
\begin{align}
a & = b + c \\
d & =e + f
\end{align}
\end{myframedeq}

\end{document}


TikZ can also make much fun:

\documentclass[11pt]{report}
\usepackage{amsmath,tikz}
\usetikzlibrary{tikzmark}
\begin{document}

\begin{tikzpicture}[remember picture,overlay]
\draw[fill=blue!10]([yshift=0pt]{pic cs:start}) rectangle ([yshift=.5em]{pic cs:end});
\end{tikzpicture}

\tikzmark{start}
\begin{align}
a &= b+c \\
d &= e+f
\end{align}\hfill\tikzmark{end}

\end{document}


You can leave or drop the [fill=blue!10] to get the following outputs: