答案1
你可以使用 tikz:
\documentclass{beamer}
\usepackage{tikz}
\setbeamertemplate{background canvas}{
\begin{tikzpicture}[overlay,remember picture,inner sep=0pt,outer sep=0pt]
\draw[blue,dash=on 20pt off 10pt phase 0pt,line width=0.3cm] (current page.south west) rectangle (current page.north east);
\end{tikzpicture}
}
\begin{document}
\begin{frame}
abc
\end{frame}
\end{document}