Arrows on Parallelogram

Question

Got this code from the website tried for hours to adopt it all I want to do is change the arrows in the middle of the parallelogram to the normal arrows seen in most mathematical text books >> but maybe a bit larger my MWE is below.

\documentclass{scrreprt}
\usepackage{tikz}
\usetikzlibrary{decorations.markings}
\tikzset{%
    ->-/.style={decoration={markings, mark=at position 1.5 with {\arrow{>}}},
        postaction={decorate}},
    ->>-/.style={decoration={markings, mark=at position 1.0 with {\arrow{>>}}},
        postaction={decorate}},
}  
\begin{document}
\begin{tikzpicture}[meme/.pic={ \fill[red ] (150:6pt) to[bend right=10] (0:3pt) to[bend right=10] (-150:6pt)--cycle;
    }]
    \path
    (0,0) coordinate (A) 
    (2,3) coordinate (B)
    (8,3) coordinate (C)
    (6,0) coordinate (D);
\node [left] at (0,0) {D};
\node [left] at (2,3) {A};
\node [right] at (8,3) {B};
\node [right] at (6,0) {C};

\draw [thick] (2,3) -- (6,0);



\draw[sloped] (A)
--(B) pic[pos=.5]{meme}
--(C) pic[pos=.46]{meme} pic[pos=.54]{meme}
--(D) pic[pos=.5]{meme}
--cycle pic[pos=.46]{meme} pic[pos=.54]{meme};


\end{tikzpicture}
\end{document}

Answer 1

Update: The meme style from this answer is made to create a user-flexible arrow in a simple way.

Adapt to your question, just take a minor change to meme (you can put it in a \tikzset)

meme/.pic={ 
\draw (150:8pt) --(0,0)-- (-150:8pt);
}

\documentclass{scrreprt}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[meme/.pic={ 
\draw (150:8pt) --(0,0)-- (-150:8pt);
}]
\path
(0,0) coordinate (D) node[below left]{$D$} 
(2,3) coordinate (A) node[above left]{$A$}
(6,0) coordinate (C) node[below right]{$C$}
(A)+(C) coordinate (B) node[above right]{$B$};
\draw[gray] (A)--(C) (B)--(D);
\draw[thick] 
(A)--(B) pic[pos=.5,sloped,red]{meme}
(D)--(C) pic[pos=.5,sloped,red]{meme}
(D)--(A) pic[pos=.47,sloped,blue]{meme}
         pic[pos=.53,sloped,blue]{meme}
(C)--(B) pic[pos=.47,sloped,blue]{meme}
         pic[pos=.53,sloped,blue]{meme}
;
\end{tikzpicture} 
\end{document}

Do you see this simple and flexible?

---

Old: Note that a coordinate is a node without content. Maybe what you want is the Straight Barb arrow from the arrows.meta library (see more in the PGFmanual).

In Straight Barb[angle=30:8pt], the meanings of 30 and 8pt are tip angle and tip length.

\documentclass{scrreprt}
\usepackage{tikz}
\usetikzlibrary{arrows.meta}
\begin{document}
\begin{tikzpicture}[>={Straight Barb[angle=30:8pt]}]
\path
(0,0) coordinate (D) node[below left]{$D$} 
(2,3) coordinate (A) node[above left]{$A$}
(6,0) coordinate (C) node[below right]{$C$}
(A)+(C) coordinate (B) node[above right]{$B$};
\draw[blue] (2,3) -- (6,0);
\draw[->] (A)--(B);
\draw[->] (D)--(C);
\draw[->] (D)--(A);
\draw[->] (C)--(B);
\end{tikzpicture} 
\end{document}

Answer 2

I took inspiration from a quick Google search.

I prefer the arrow pic over using the decorations.markings library. The first line of its code shifts the drawing so that the middle of the whole construct is where we want it (otherwise the tips wouldn't be symmetric).

These pics are placed via an edge node style so that we don't have to write out each pic specification.

The example shows two ways to double such an arrow:

1. Using >> in the ->>- style which just adds the second arrow tip right behind the first one.
2. Using ->- which a > specification of a double arrow tip (because I want a seperation between those Bars).

Code

\documentclass[tikz]{standalone}
\usetikzlibrary{arrows.meta, quotes}
\tikzset{
  reversed/.style={xscale=-1},
  pics/arrow/.style={/tikz/sloped, /tikz/allow upside down, code=%
    \pgfarrowtotallength{#1}\tikzset{xshift/.expanded=.5*\csname pgf@x\endcsname}%
    \pgfarrowdraw{#1}}, pics/arrow/.default=>}
\begin{document}
\tikz[
  line join=round,
  Arr/.tip={Straight Barb[angle'=60, scale=2]},
  ||/.tip={Bar[sep] . Bar},
  > = Arr,
  ->-/.style={edge node={pic[#1]{arrow}}},
  ->>-/.style={edge node={pic[#1]{arrow=>>}}},
] \draw[thick, draw=purple]
                       (0, 0) coordinate["$D$" left]  (D)
     to[->>-]          (2, 3) coordinate["$A$" left]  (A)
     to[->-]           (8, 3) coordinate["$B$" right] (B)
     to[->>-=reversed] (6, 0) coordinate["$C$" right] (C)
     to[->- =reversed] cycle
     coordinate["$E$"] (E) at (intersection of D--B and A--C)
     [behind path, every edge/.append style={black, thin}, arrows={[slant=.2]}]
     (A) edge[>=||, ->-=near start, ->-=near end] (C)
     (B) edge[>=|,  ->-=near start, ->-=near end] (D);
\end{document}

Output