\documentclass{standalone}
\usepackage{tikz}
\usepackage{dimer_example}

\begin{document}
\hfil\begin{tikzpicture}
\basegraph

\draw[line width=3pt](A2)--(A3);
\draw[line width=3pt](A1)--(D4);
\draw[line width=3pt](D3)--(D2);
\draw[line width=3pt](A8)--(D1);
\draw[line width=3pt](C1)--(A4);
\draw[line width=3pt](A5)--(A6);
\draw[line width=3pt](A7)--(B3);
\draw[line width=3pt](B1)--(B2);

\end{tikzpicture}

\end{document}