# Where to find the definition of a given beamer theme?

I want to modify a detail in the header/footer lines of a beamer theme that I am using (for instance Antibes). Where can I find the corresponding definition file, to copy the existing definition of the header-footer lines?

Antibes uses the tree outer theme. You can find the definition of its headline in beamerouterthemetree.sty:

\defbeamertemplate*{headline}{tree theme}
{%
\end{beamercolorbox}
\begin{beamercolorbox}[wd=\paperwidth,ht=2.5ex,dp=1.125ex,%
\end{beamercolorbox}
\begin{beamercolorbox}[wd=\paperwidth,ht=2.5ex,dp=1.125ex,%
\ifbeamer@tree@showhooks
\ifdim\wd\beamer@tempbox>1pt%
\hskip2pt\raise1.9pt\hbox{\vrule width0.4pt height1.875ex\vrule width 5pt height0.4pt}%
\hskip1pt%
\fi%
\else%
\hskip6pt%
\fi%
\end{beamercolorbox}
\begin{beamercolorbox}[wd=\paperwidth,ht=2.5ex,dp=1.125ex,%
\ifbeamer@tree@showhooks
\ifdim\wd\beamer@tempbox>1pt%
\hskip9.4pt\raise1.9pt\hbox{\vrule width0.4pt height1.875ex\vrule width 5pt height0.4pt}%
\hskip1pt%
\fi%
\else%
\hskip12pt%
\fi%