using linestyle and color of \tikzlastnode in append after command

I want the atom symbol color and style below to be the same as the enclosing node style; how do I do it? Is there a way to reference the linestyle of \tikzlastnode?

\documentclass[border=3mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning, calc}
\begin{document}
\title{science symbol}
\begin{tikzpicture}[>=latex,
font=\sffamily,
atom/.style = {circle, minimum size=#1,
append after command={%
\pgfextra{
\foreach \ang in {0,120,240}
\draw[rotate around={\ang:(0,0)}] (\tikzlastnode.center) ellipse (0.45*#1 and 0.15*#1);
\fill (\tikzlastnode.center) circle (0.05*#1);
}
}
}
]

\node[draw, atom=10mm] (C1) at (0,0){};
\node[draw, very thin, red, atom=10mm] (C2) at (2cm,0){};
\node[draw, thick, green, atom=10mm] (C3) at (2cm,2cm){};
\draw[->] (C1) -- (C2);
\draw[->] (C1) -- (C3);

\end{tikzpicture}
\end{document}


I muddled my own way through this again, and found an alternative approach using \pgfdeclareshape rather than append after command. (why does it always feel like a painful victory when I do this sort of thing???) Other reference questions I used were

but it was basically just how to use \pgfdeclareshape to work from the circle shape, see https://svn.ssec.wisc.edu/repos/geoffc/LaTeX/beamerposter_UW-SSEC/pgfmoduleshapes.code.tex for source code.

\documentclass[border=3mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning, calc}
\begin{document}
\title{science symbol}
\pgfdeclareshape{atomshape}{%
\inheritsavedanchors[from=circle]%
\inheritanchorborder[from=circle]%
\inheritanchor[from=circle]{center}%
%
\backgroundpath{%
\pgfusepath{fill}
\foreach\ang in {0,120,240}{
\pgftransformrotate{\ang}
\pgfpathellipse{\pgfpointorigin}
}
}%
}
\begin{tikzpicture}[>=latex,
font=\sffamily,
atom/.style = {atomshape, minimum size=#1}
]

\node[draw, atom=10mm] (C1) at (0,0){};
\node[draw, very thin, red, atom=10mm] (C2) at (2cm,0){};
\node[draw, thick, green, atom=10mm] (C3) at (2cm,2cm){};
\draw[->] (C1) -- (C2);
\draw[->] (C1) -- (C3);

\end{tikzpicture}
\end{document}