Framing a colored box with an image

Question

I have a color box (made with tcolorbox) that holds text, and I want to frame it. Unfortunately, I'm copying a style so I can't use a normal border. The border I want is only on the sides of the box with a dot at each end.

(Like this but black)

I've seen threads on here before that say you can overlay tikz drawings ontop of tcolorboxes, but that won't work. If what I want to accomplish isn't possible, I'll end up using that but I'd prefer to use an image. Since it's a class, I want it to be as lightweight as possible.

There are two problems. For one, I don't know how to position images overtop something like a tcolorbox. The second problem is that the height of these boxes is variable (based on the text). I don't want to stretch the border image because I want the dots to remain circle, but I want the actual border part to elongate.

So my actual question:

1) How do I position a graphic precisely following a border (corner as an anchor)?

2) How can I scale my image vertically without stretching the image?

---

Minimum working example:

\documentclass[10pt,oneside,twocolumn]{book}
\usepackage{tcolorbox}
\usepackage{xcolor}
\usepackage{lipsum}

\definecolor{textbox}{HTML}{D5D2DD}

\newtcolorbox{textbox}{
  colframe=textbox,
  colback=textbox,
  top=1mm, bottom=1mm, left=1.5mm, right=1.5mm,
  arc=0mm,
}

\begin{document}
  \raggedright

  \lipsum[1]

  \hfill
  \begin{textbox}
    \lipsum[2]  
  \end{textbox}
  \hfill

  \lipsum[3]

  \hfill
  \begin{textbox}
    \lipsum[4-5]  
  \end{textbox}
  \hfill

  \lipsum[6] 

\end{document}

---

Standalone of border:

\documentclass{standalone}
\usepackage{tikz}

\begin{document}
  \begin{tikzpicture}
    %\draw[help lines] (-1,-2) grid (1,2);

    \node[circle,fill=black,inner sep=1pt] at (0,2) {};
    \draw[thick] (0,2) -- (0,-2);
    \node[circle,fill=black,inner sep=1pt] at (0,-2) {};
  \end{tikzpicture}
\end{document}

Answer 1

You say that overlaying tikz drawings won't work, but it seems to work OK. You can use the remember and overlay options for enhanced boxes if you load the skins library.

\documentclass[10pt,oneside,twocolumn]{book}
\usepackage{lipsum}
\usepackage{tcolorbox}
\tcbuselibrary{skins}
\definecolor{textbox}{HTML}{D5D2DD}

\newtcolorbox{textbox}{
  enhanced,
  remember,
  colframe=textbox,
  colback=textbox,
  top=1mm, bottom=1mm, left=1.5mm, right=1.5mm,
  arc=0mm,
  overlay={
    \node (nw) [circle,fill=black,inner sep=1pt,xshift=4pt,yshift=-4pt]
      at (frame.north west) {};
    \node (sw) [circle,fill=black,inner sep=1pt,xshift=4pt,yshift=4pt]
      at (frame.south west) {};
    \node (ne) [circle,fill=black,inner sep=1pt,xshift=-4pt,yshift=-4pt]
      at (frame.north east) {};
    \node (se) [circle,fill=black,inner sep=1pt,xshift=-4pt,yshift=4pt]
      at (frame.south east) {};
    \draw[thick] (nw) -- (sw);
    \draw[thick] (ne) -- (se);
  }
}
\begin{document}
\raggedright

\lipsum[1]

\hfill
\begin{textbox}
  \lipsum[2]  
\end{textbox}
\hfill

\lipsum[3]

\hfill
\begin{textbox}
  \lipsum[4-5]  
\end{textbox}
\hfill

\lipsum[6] 
\end{document}