Add big quotation marks inside my colorbox

Question

I have this code (MWE):

\documentclass{article}
\usepackage{tikz,lmodern}
\usepackage[most]{tcolorbox}

\newtcbtheorem{theo}%
  {Definition}{fonttitle=\bfseries\upshape, 
     arc=0mm, colback=blue!5!white,colframe=blue!75!black}{theorem}

\begin{document}

\begin{theo}{Translationally ordered structure}{transtructure}
``A translationally ordered structure is a structure whose scattering amplitude [structure factor] is given by a discrete sum of Bragg peaks'' 
\end{theo}

\end{document}

that produces this:

I would like to add e.g. this vector graphics big quotation marks to make my box look like this:

How can I do it?

Answer 1

Like this?

\documentclass{article}
\usepackage{tikz,lmodern}
\usepackage[most]{tcolorbox}

\newtcbtheorem{theo}%
  {Definition}{fonttitle=\bfseries\upshape, 
     arc=0mm,enhanced, 
     underlay={%
        \begin{tcbclipinterior}
            \fill [blue!5!white]
              (interior.south west) rectangle (interior.north east);
             \node[opacity=0.4,scale=4,anchor=north west,inner sep=0.2pt,
             font=\bfseries] at 
             (interior.north west) {``};
             \node[opacity=0.4,scale=4,anchor=south east,inner sep=0.2pt,
             font=\bfseries] at 
             ([yshift=-3ex]interior.south east) {''};
        \end{tcbclipinterior}},% colback=blue!5!white,
        before upper=\hspace*{1em},after upper=\hspace*{1em},
        colframe=blue!75!black}{theorem}

\begin{document}

\begin{theo}{Translationally ordered structure}{transtructure}
A translationally ordered structure is a structure whose scattering amplitude
[structure factor] is given by a discrete sum of Bragg peaks.
\end{theo}

\end{document}

You can modify it, of course. For example

\documentclass{article}
\usepackage{tikz,lmodern}
\usepackage[most]{tcolorbox}

\newtcbtheorem{theo}%
  {Definition}{fonttitle=\bfseries\upshape, 
     arc=0mm,enhanced, 
     underlay={%
        \begin{tcbclipinterior}
            \fill [blue!5!white]
              (interior.south west) rectangle (interior.north east);
             \node[opacity=0.3,xscale=5,yscale=4,anchor=north west,inner sep=0.1pt,
             font=\bfseries] at 
             (interior.north west) {`\hspace*{-0.1em}`};
             \node[opacity=0.3,xscale=5,yscale=4,anchor=south east,inner sep=0.1pt,
             font=\bfseries] at 
             ([yshift=-3ex]interior.south east) {'\hspace*{-0.1em}'};
        \end{tcbclipinterior}},% colback=blue!5!white,
        before upper=\hspace*{1em},after upper=\hspace*{1em},
        colframe=blue!75!black}{theorem}

\begin{document}

\begin{theo}{Translationally ordered structure}{transtructure}
A translationally ordered structure is a structure whose scattering amplitude
[structure factor] is given by a discrete sum of Bragg peaks.
\end{theo}

\end{document}

And you can include any graphics you want instead of the text nodes. My problem with the link you suggest is that I do not know if I am legally allowed to use the graphics from that link.