\documentclass[preview]{standalone}

\usepackage{tikz}
\usetikzlibrary{calc} %for coordinate calculation
\usetikzlibrary{math} %for \tikzmath (thanks to /u/tzjin for the LaTeX Challenge Part 2 where I learned about this!)

\begin{document}
    \begin{tikzpicture}
        \tikzmath{
            \N = 30; %the number of lines to draw per side, more is prettier but 30 is a good number for the challenge (I suggest trying 50 or greater)
            \L = 10; %width of the side, only affects the output size
            \d = \L/\N; %distance between line connection points (on both horizontal and vertical axes)
            \lineW = 0.1; %width of the lines, should be small for the best output
            \lineopac = 1; %opacity of the lines
        }

        \coordinate (LL) at (0,0); %lower left corner
        \coordinate (LR) at (\L,0); %lower right corner
        \coordinate (UR) at (\L,\L); %upper right corner
        \coordinate (UL) at (0,\L); %upper left corner

        \coordinate (dx) at (\d,0); %for coordinate calculations
        \coordinate (dy) at (0,\d); %for coordinate calculations

        \foreach \i in {0,...,\N}{
            \draw[draw opacity = \lineopac, line width = \lineW] ($(UL) - \i*(dy)$) -- ($(LL) + \i*(dx)$);
            \draw[draw opacity = \lineopac, line width = \lineW] ($(LR) + \i*(dy)$) -- ($(UR) - \i*(dx)$);
        }
    \end{tikzpicture}
\end{document}