extra-01-example-tikz.md

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{tikz}
\usetikzlibrary{perspective}

\begin{document}

\newcommand\simplecuboid[3]{%
\fill[gray!80!white] (tpp cs:x=0,y=0,z=#3)
-- (tpp cs:x=0,y=#2,z=#3)
-- (tpp cs:x=#1,y=#2,z=#3)
-- (tpp cs:x=#1,y=0,z=#3) -- cycle;
\fill[gray] (tpp cs:x=0,y=0,z=0)
-- (tpp cs:x=0,y=0,z=#3)
-- (tpp cs:x=0,y=#2,z=#3)
-- (tpp cs:x=0,y=#2,z=0) -- cycle;
\fill[gray!50!white] (tpp cs:x=0,y=0,z=0)
-- (tpp cs:x=0,y=0,z=#3)
-- (tpp cs:x=#1,y=0,z=#3)
-- (tpp cs:x=#1,y=0,z=0) -- cycle;}
\newcommand{\simpleaxes}[3]{%
\draw[->] (-0.5,0,0) -- (#1,0,0) node[pos=1.1]{$x$};
\draw[->] (0,-0.5,0) -- (0,#2,0) node[pos=1.1]{$y$};
\draw[->] (0,0,-0.5) -- (0,0,#3) node[pos=1.1]{$z$};}
\begin{tikzpicture}[3d view]
   \simplecuboid{2}{2}{2}
   \simpleaxes{2}{2}{2}
\end{tikzpicture}
\end{document}