using linestyle and color of \tikzlastnode in append after command

Question

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}

Answer 1

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

• Size of circle path vs. circle node in \pgfdeclareshape?
• How to retrieve current stroke and fill color in PGF/TikZ

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{%
    \pgfpathcircle{\pgfpointorigin}{0.1*\radius}
    \pgfusepath{fill}
    \pgfpathcircle{\pgfpointorigin}{\radius}%
    \foreach\ang in {0,120,240}{
      \pgftransformrotate{\ang}
      \pgfpathellipse{\pgfpointorigin} 
                 {\pgfpoint{0.9*\radius}{0cm}} 
                 {\pgfpoint{0cm}{0.3*\radius}}
    }
  }%
}
\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}