https://tex.stackexchange.com/a/146682

s/texsx/laas

beamercolorthemelaas.sty

+\mode<presentation>
+
+% Settings
+\setbeamercolor*{title page header}{fg=white}
+\setbeamercolor*{author}{fg=white}
+\setbeamercolor*{date}{fg=white}
+\setbeamercolor*{item}{fg=orange}
+
+\mode
+<all>

beamerinnerthemelaas.sty

+\mode<presentation>
+
+\setbeamertemplate{background}{
+  \begin{tikzpicture}
+  \useasboundingbox (0,0) rectangle(\the\paperwidth,\the\paperheight);
+  \fill[color=brown] (0,2) rectangle (\the\paperwidth,\the\paperheight);
+  \fill[color=orange] (0,0) rectangle(2.95,1.9);
+  \fill[color=blue!50!cyan!80] (3.05,0) rectangle(\the\paperwidth,1.9);
+  \ifnum\thepage>1\relax%
+   \fill[white,opacity=1] (0,0) rectangle(\the\paperwidth,\the\paperheight);
+   \fi
+  \end{tikzpicture}
+}
+
+% Title page
+\defbeamertemplate*{title page}{laas}[1][]
+{
+   \vskip6cm%
+    \begin{beamercolorbox}[wd=12cm,leftskip=3cm,sep=8pt,#1]{title page header}
+      \usebeamerfont{title}\inserttitle\par%
+    \end{beamercolorbox}%
+    \vskip0.75cm%
+    \begin{beamercolorbox}[wd=12cm,leftskip=3cm,#1]{author}
+      \usebeamerfont{author}\insertauthor%
+    \end{beamercolorbox}
+     \vskip0.2cm%
+    \begin{beamercolorbox}[wd=12cm,leftskip=3cm,#1]{date}
+      \usebeamerfont{author}\insertdate%
+    \end{beamercolorbox}
+  \vfill
+}
+
+% Items
+\setbeamertemplate{items}[square]
+\setbeamertemplate{sections/subsections in toc}[square]
+
+\mode
+<all>

beamerouterthemelaas.sty

+\mode<presentation>
+
+% Frame title
+\defbeamertemplate*{frametitle}{laas}[1][]
+{
+\vskip1cm%
+  \begin{beamercolorbox}[wd=\paperwidth,ht=1.2cm]{frametitle}
+  \begin{tikzpicture}
+  \useasboundingbox[fill=white](0,0) rectangle(\the\paperwidth,1.2);
+  \fill[orange] (0,0) rectangle(2.95,1.2);
+  \fill[blue!50!cyan!80] (3.05,0) rectangle(\the\paperwidth,1.2);
+   \ifx\insertframesubtitle\@empty%
+      {\node[anchor=west, white,font=\large] at (3.2,0.61){\insertframetitle};}
+      \else%
+      {\node[anchor= west, white,font=\large] at (3.2,0.81){\insertframetitle};%
+       \node[anchor= west, white,font=\small] at (3.2,0.41){\insertframesubtitle};}%
+      \fi
+  \end{tikzpicture}
+  \end{beamercolorbox}
+}
+
+\mode<all>

beamerthemelaas.sty

+\mode<presentation>
+
+% Requirement
+\RequirePackage{tikz}
+
+% Settings
+\useinnertheme{laas}
+\useoutertheme{laas}
+\usecolortheme{laas}
+
+\setbeamertemplate{navigation symbols}{}
+%\setbeamertemplate{blocks}[rounded][shadow=true]
+
+\mode<all>

example.tex

+\documentclass{beamer}
+\usepackage[utf8]{inputenc}
+\usepackage[T1]{fontenc}
+\title{There Is No Largest Prime Number}
+\date[ISPN ’80]{27th International Symposium of Prime Numbers}
+\author[Euclid]{Euclid of Alexandria \texttt{euclid@alexandria.edu}}
+
+\usetheme{laas}
+
+\begin{document}
+
+\begin{frame}
+\titlepage
+\end{frame}
+
+
+\begin{frame}
+\frametitle{There Is No Largest Prime Number}
+\framesubtitle{The proof uses \textit{reductio ad absurdum}.}
+\begin{theorem}
+There is no largest prime number. \end{theorem}
+\begin{enumerate}
+\item<1-| alert@1> Suppose $p$ were the largest prime number.
+\item<2-> Let $q$ be the product of the first $p$ numbers.
+\item<3-> Then $q+1$ is not divisible by any of them.
+\item<1-> But $q + 1$ is greater than $1$, thus divisible by some prime
+number not in the first $p$ numbers.
+\end{enumerate}
+\end{frame}
+
+\begin{frame}{A longer title}
+\begin{itemize}
+\item one
+\item two
+\end{itemize}
+\end{frame}
+
+\end{document}