Need help getting tcolorbox right

Question

I'm trying to make a shaped box to hold arbitrary content and I'm using tcolorbox with code I adapted for my purposes from another question. So far I have:

\documentclass[20pt, a4paper]{article}

\usepackage{color}
\usepackage{tcolorbox}
\usepackage{lipsum}

\tcbuselibrary{skins}
\usetikzlibrary{calc}
\pgfdeclarelayer{background}
\pgfdeclarelayer{foreground}
\pgfsetlayers{background,main,foreground}

\newtcolorbox{mybox}{
    left=15pt,
    top=15pt,
    bottom=15pt,
    right=15pt,
    skin=freelance,
    frame code={%
        \begin{pgfonlayer}{background}
            \draw[line width=4pt,color=purple,fill=purple]($(frame.north west) + (15pt, 0pt)$)
                -- (frame.north east)
                -- ($(frame.south east) + (0pt, 15pt)$)
                -- ($(frame.south east) + (-15pt, 0pt)$)
                -- (frame.south west)
                -- ($(frame.north west) + (0pt, -15pt)$)
                -- cycle;

        \end{pgfonlayer}
    },
}

\begin{document}

\begin{mybox}
\lipsum[1]
\end{mybox}

\end{document}

I would like some way to fully fill the shape formed with a solid color without going outside the lines, but behind the content to be displayed. Using the colback option creates a rounded rectangle box of color that goes outside the lines at points and doesn't quite reach the corners at others. However if I try and use the fill option for the shape then it is either filled and blocking out the text, or entirely behind the background color box (depending on which layer I put the frame code on).

Answer 1

Basically the same method has to be applied for interior code, with adjusted vertices, however!

\documentclass[20pt, a4paper]{article}


\usepackage[skins]{tcolorbox}
\usepackage{lipsum}

\usetikzlibrary{calc}
\pgfdeclarelayer{background}
\pgfdeclarelayer{foreground}
\pgfsetlayers{background,main,foreground}

\newtcolorbox{mybox}{%
    left=15pt,
    top=15pt,
    bottom=15pt,
    right=15pt,
    skin=enhanced jigsaw,
    frame code={%
      \begin{pgfonlayer}{background}
        \draw[line width=4pt,color=purple,fill=purple]($(frame.north west) + (15pt, 0pt)$)
        -- (frame.north east)
        -- ($(frame.south east) + (0pt, 15pt)$)
        -- ($(frame.south east) + (-15pt, 0pt)$)
        -- (frame.south west)
        -- ($(frame.north west) + (0pt, -15pt)$)
        -- cycle;
      \end{pgfonlayer}
    },
    interior code={%
      \draw[line width=4pt,color=purple,fill=white!90!black]($(frame.north west) + (15pt, -4pt)$) -- ($(frame.north east) + (-4pt,-4pt)$) 
      -- ($(frame.south east) + (-4pt, 15pt)$)  
      -- ($(frame.south east) + (-15pt, 4pt)$)
      -- ($(frame.south west) + (4pt, 4pt)$)
      -- ($(frame.north west) + (4pt, -15pt)$)
      -- cycle;
    }
}

\begin{document}

\begin{mybox}
\lipsum[1]
\end{mybox}

\end{document}