Custom enumerate environment inside Fancybox

Question

I would like to put a enumerate environment (customized with the enumitem package) inside of a shadowbox created from the Fancybox package. Here's my MWE:

\documentclass[letterpaper,10pt,american]{article}
\usepackage[left=1 in, right=1 in, top=1 in, bottom=1 in]{geometry}
\usepackage{amsmath,amsfonts,amssymb,amsthm,color,hyperref,enumitem}
\usepackage{setspace}
\usepackage{caption}
\usepackage{pgf,tikz}
\usetikzlibrary{automata,arrows,positioning,calc,decorations.pathreplacing}
\usepackage{fancybox}
\begin{document}
\shadowbox{
\begin{enumerate}[before=\itshape,font=\normalfont,label=\textbf{ABC.\arabic*}]
\item Item 1
\item Item 2
\item Item 3
\end{enumerate}}
\end{document}

However, the customization of my enumerate environment doesn't show up: only numbers 1., 2., 3. are displayed, rather than ABC.1, ABC.2, ABC.3. Am I doing something wrong? What's causing enumitem customization not to work inside fancybox?

EDIT: We've almost solved the issue! But there's still one small obstacle remaining to fix: When you have ten or more items in the list, then ABC.10, ABC.11, ABC.12, etc. will leak outside of the box.

Answer 1

Some improvements to @Harish Kumar's solution: enumitem has the tools to solve the leak problem for long labels: the key wide= and widest=.

There is also a problem in case of long items: the box leaks into the right margin. I propose 3 solutions for 3 different layouts: one with an indent on both sides, another where only the shadow leaks into the right margin, and no leak at all. Also, I simplified your code for the margins, since they're all equal, and used the showframe option to demonstrate what happens:

\documentclass[letterpaper,10pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[margin=1 in, showframe]{geometry}
\usepackage{enumitem}
\usepackage{fancybox}
\usepackage{varwidth}
\begin{document}

\shadowbox{%
  \begin{varwidth}{\dimexpr\linewidth-2\fboxsep-\shadowsize-\parindent\relax}
    \begin{enumerate}[before=\itshape,wide = 0pt, font=\normalfont,label=\textbf{ABC.\arabic*}]
      \item Item 1\setcounter{enumi}{99}
      \item Item 2 \emph{This one’s a very long item. This one’s a very long item. This one’s a very long item. This one’s a very long item.}
      \item Item 3
    \end{enumerate}
  \end{varwidth}
}
\vskip1cm
\noindent\shadowbox{%
  \begin{varwidth}{\dimexpr\linewidth-2\fboxsep-2\shadowsize\relax}
    \begin{enumerate}[before=\itshape,wide = 0pt, font=\normalfont, leftmargin =*, label=\textbf{ABC.\arabic*},widest =999]
      \item Item 1\setcounter{enumi}{99}
      \item Item 2. \emph{This one’s a very long item. This one’s a very long item. This one’s a very long item. This one’s a very long item.}
      \item Item 3
    \end{enumerate}
  \end{varwidth}
}
\vskip1cm
\noindent\shadowbox{%
  \begin{varwidth}{\dimexpr\linewidth-2\fboxsep-\shadowsize\relax}
    \begin{enumerate}[before=\itshape,wide = 0pt, font=\normalfont, leftmargin =*, label=\textbf{ABC.\arabic*},widest =999]
      \item Item 1\setcounter{enumi}{99}
      \item Item 2. \emph{This one’s a very long item. This one’s a very long item. This one’s a very long item. This one’s a very long item.}
      \item Item 3
    \end{enumerate}
  \end{varwidth}
}
\end{document} 

Answer 2

Here's a breakable version with tcolorbox as an alternative:

\documentclass[letterpaper,10pt,american]{article}
\usepackage[left=1 in, right=1 in, top=1 in, bottom=1 in]{geometry}
\usepackage{amsmath,amsfonts,amssymb,amsthm,color,enumitem}


\usepackage{setspace}
\usepackage{caption}
\usepackage{pgf,tikz}
\usetikzlibrary{automata,arrows,positioning,calc,decorations.pathreplacing}
%\usepackage{fancybox}
\usepackage[most]{tcolorbox}
\usepackage{xpatch}

\newtcolorbox{enumshadebox}[1][]{breakable, enhanced jigsaw,sharp corners, colframe=black,drop shadow,boxsep=5pt,#1}
\usepackage{hyperref}



\begin{document}

\begin{enumshadebox}
\begin{enumerate}[leftmargin=50pt,before=\itshape,font=\normalfont,label=\textbf{ABC.\arabic*},widest={ABC.100}]
\foreach \x in {1,...,60} {%
  \item \x
}
\end{enumerate}
\end{enumshadebox}

\end{document}

Answer 3

You have to use enumerate inside a minipage. If you want a tight box, use varwidth package. Use leftmargin=* in addition.

\documentclass[letterpaper,10pt]{article}
\usepackage[left=1 in, right=1 in, top=1 in, bottom=1 in]{geometry}
\usepackage{enumitem}
\usepackage{fancybox}
\usepackage{varwidth}
\begin{document}
\shadowbox{%
\begin{varwidth}{\linewidth}
\begin{enumerate}[before=\itshape,leftmargin=*,font=\normalfont,label=\textbf{ABC.\arabic*}]
\item Item 1
\item Item 2
\item Item 3
\end{enumerate}
\end{varwidth}
}
\end{document}