I have just started learning some TeX programming and am learning TikZ in plain TeX. My question is why is the following not working as intended; I try to define `\sty` as the TikZ drawing parameter, but it does not seem to be working.

```
\nopagenumbers
\input tikz.tex

\def\center#1\endcenter{\centerline{#1}}

\def\sty{step=.5cm,gray,very thin}
This is my first plain \TeX\ file. Let me try some commands below:
\vskip 1cm
\center
\tikzpicture[scale=3]
\draw [\sty] (-1.4,-1.4) grid (1.4,1.4);
\draw [->](-1.5,0) -- (1.5,0);
\draw [->](0,-1.5) -- (0,1.5);
\draw (0,0) circle [radius=1cm];
\path[fill,draw][fill=green!20!white, draw=green!50!black] (0,0) -- (3mm,0mm) arc [start angle=0, end angle=30, radius=3mm] -- cycle;
\endtikzpicture
\endcenter

\bye

```

Maybe it has to do with the order TeX documents are compiled/parsed. I am not sure though.