Boxes in matrices using tikz

I have drawn this matrix with tikz but as you can see the boxes are not sqares. How could I fix this? I defined

\usepackage{tikz}
\usetikzlibrary{arrows,matrix,positioning}
\newcommand\bigzero{\makebox(0,0){\text{\huge0}}}


followed by my matrix

$$\label{eqn:mat} \begin{tikzpicture}[baseline=(current bounding box.center)] \matrix [matrix of math nodes,left delimiter=(,right delimiter=)] (m) { 0&1\\ -1&0&&&&\bigzero\\ &&0&1\\ &&-1&0\\ &&&&\ddots\\ &\bigzero&&&&0&1\\ &&&&&-1&0\\ }; \draw (m-1-1.north west) -- (m-1-2.north east) -- (m-2-2.south east) -- (m-2-1.south west) -- (m-1-1.north west); \draw (m-3-3.north west) -- (m-3-4.north east) -- (m-4-4.south east) -- (m-4-3.south west) -- (m-3-3.north west); \draw (m-6-6.north west) -- (m-6-7.north east) -- (m-7-7.south east) -- (m-7-6.south west) -- (m-6-6.north west); \end{tikzpicture}$$

• You can use fit like in the answer to your previous question. If you really need squares, you may load shapes.geometric and use a regular polygon,regular polygon sides=4 for the fit. Note that the arrows library got superseded by arrows.meta. – user121799 Sep 9 '18 at 21:34

\documentclass{article}
$$\label{eqn:mat} \begin{tikzpicture}[baseline=(current bounding box.center)] \matrix [matrix of math nodes,left delimiter=(,right delimiter=)] (m) { 0&1\\ -1&0&&&&\bigzero\\ &&0&1\\ &&-1&0\\ &&&&\ddots\\ &\bigzero&&&&0&1\\ &&&&&-1&0\\ }; \node[draw,fit=(m-1-1) (m-2-2),inner sep=0pt]{}; \node[draw,fit=(m-3-3) (m-4-4),inner sep=0pt]{}; \node[draw,fit=(m-6-6) (m-7-7),inner sep=0pt]{}; \end{tikzpicture}$$