This is a VERY simple and minimalistic beamer theme, even reminiscent of marker pens on transparencies!
It mimics the look of the "seminar" package, which can only be used with plain TeX.
There are also some comments and example to show how to customise various elements, e.g. the font and colours.
%%%% This Beamer example was created by LianTze Lim, April 2017.
%%%% This is a VERY simple and minimalistic beamer theme,
%%%% even reminiscent of marker pens on transparencies!
%%%% It mimics the look of the "seminar" package, which
%%%% can only be used with plain TeX.
%%%% There are also some comments and example to show how
%%%% to customise various elements, e.g. the font and colours.
\documentclass[12pt]{beamer}
%% If you'd like the default font size to be even larger, use 14pt or 17pt; these are supported by Beamer.
\usepackage[english]{babel}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% These lines should usually go into a .sty file,
% but I'll leave them here so that it's easier to
% see how to customise a Beamer theme.
% Remember, the Beamer manual is your friend!!
% http://texdoc.net/pkg/beamer
%
%% So if your re-definitions have a @ somewhere, you
%% _MUST_ put a \makeatletter before these lines and then
%% \makeatother after them. This trick can only be done
%% in the preamble! BUT if you're doing these re-definitions
%% in a .sty file (so that you \usepackage it later), you
%% don't need the \makeatletter and \makeatother.
\makeatletter
%% Set the left and right margins
\setbeamersize{text margin left=1em,text margin right=1em}
%% FONTS
\setbeamerfont{title}{series=\bfseries,size=\LARGE}
\setbeamerfont{subtitle}{series=\bfseries,size=\Large}
\setbeamerfont{frametitle}{series=\bfseries,size=\small}
\setbeamerfont{block title}{series=\bfseries,size=\normalsize}
\setbeamerfont{footline}{size=\normalsize}
%% COLOURS
%% If you'd like everything to have the same colour
\usebeamercolor{structure}
\setbeamercolor{normal text}{fg=structure.fg}
%% Add a line after the frametitle
\addtobeamertemplate{frametitle}{}{\vspace*{-1ex}\rule{\textwidth}{1pt}}
%% Use circular discs as itemized list markers;
%% there's an existing option in Beamer for it so I'll use it
\setbeamertemplate{itemize items}[circle]
%% Remove default navigation symbols (We'll add the ones we need in the footline
\setbeamertemplate{navigation symbols}{}
%% And before the footline... actually we'd like to re-define
%% the footline
\setbeamertemplate{footline}{%
%% Beamer headlines and footlines are always full-paperwidth, so if you want the horizontal line to
%% not span it entirely you'll need to do a bit of arithmetic
\centering
\begin{minipage}{\dimexpr\paperwidth-\beamer@leftmargin-\beamer@rightmargin\relax}
\centering
\rule{\linewidth}{1pt}\vskip2pt
\usebeamerfont{footline}%
\usebeamercolor{footline}%
%% The frame number smack in the middle
\hfill\insertpagenumber/\inserttotalframenumber
\hfill%
%% ONLY the navigation symbols we want at the far right.
%% We use an \llap so that it takes up zero width, and doesn't throw the page number off-centre!
\llap{\insertframenavigationsymbol\insertbackfindforwardnavigationsymbol}\par
\end{minipage}\vskip2pt
}
\makeatother
%%%% END STYLE CUSTOMISATION %%%%%%%%%%%%
\title{A Really Simple, Minimalistic Beamer Theme}
\subtitle{because sometimes you just want something simple}
\author{LianTze Lim}
\institute{Overleaf}
\date{April 2017}
\begin{document}
\begin{frame}
\titlepage
\end{frame}
% Uncomment these lines for an automatically generated outline.
%\begin{frame}{Outline}
% \tableofcontents
%\end{frame}
\section{Introduction}
\begin{frame}{Introduction}
\begin{itemize}
\item Your introduction goes here!
\item Use \texttt{itemize} to organize your main points.
\end{itemize}
\vskip 1cm
\begin{block}{Examples}
Some examples of commonly used commands and features are included, to help you get started.
\end{block}
\end{frame}
\section{Some \LaTeX{} Examples}
\subsection{Tables and Figures}
\begin{frame}{Tables and Figures}
\begin{itemize}
\item Use \texttt{tabular} for basic tables --- see Table~\ref{tab:widgets}, for example.
\item You can upload a figure (JPEG, PNG or PDF) using the files menu.
\item To include it in your document, use the \texttt{includegraphics} command (see the comment below in the source code).
\end{itemize}
% Commands to include a figure:
%\begin{figure}
%\includegraphics[width=\textwidth]{your-figure's-file-name}
%\caption{\label{fig:your-figure}Caption goes here.}
%\end{figure}
\begin{table}
\centering
\begin{tabular}{l|r}
Item & Quantity \\\hline
Widgets & 42 \\
Gadgets & 13
\end{tabular}
\caption{\label{tab:widgets}An example table.}
\end{table}
\end{frame}
\subsection{Mathematics}
\begin{frame}{Readable Mathematics}
Let $X_1, X_2, \ldots, X_n$ be a sequence of independent and identically distributed random variables with $\text{E}[X_i] = \mu$ and $\text{Var}[X_i] = \sigma^2 < \infty$, and let
$$S_n = \frac{X_1 + X_2 + \cdots + X_n}{n}
= \frac{1}{n}\sum_{i}^{n} X_i$$
denote their mean. Then as $n$ approaches infinity, the random variables $\sqrt{n}(S_n - \mu)$ converge in distribution to a normal $\mathcal{N}(0, \sigma^2)$.
\end{frame}
\end{document}