documentclass[border=2mm,tikz]{standalone}
usepackage{tikz}
usepackage{tikz-3dplot}

begin{document}

tdplotsetmaincoords{70}{70}
begin{tikzpicture}[tdplot_main_coords,font=sffamily]

draw[-latex] (-7.5,0,0) -- (7.5,0,0)  node[above right]  {$x$};
draw[-latex] (0,-7.5,0) -- (0,7.5,0)  node[below] {$y$};
draw[-latex] (0,0,-7.5) -- (0,0,7.5)  node[above left]  {$z$};

draw[fill=gray,opacity=0.4] (0,-7.5,7.5) -- (0,7.5,7.5) -- (0,7.5,-7.5) -- (0,-7.5,-7.5) -- cycle;
draw[fill=gray,opacity=0.2] (-7.5,0,-7.5) -- (-7.5,0,7.5) -- (7.5,0,7.5) -- (7.5,0,-7.5) -- cycle;

end{tikzpicture}

end{document}