\documentclass[11pt]{beamer}
\usepackage[T5]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[english, vietnamese]{babel}
\usepackage{lmodern}
\usepackage{amsmath, amssymb, booktabs, graphicx, hyperref}

% Theme and color setup
\usetheme{Madrid}
\usecolortheme{default}

% Color scheme
\newcommand{\red}[1]{\textcolor{red}{#1}}
\newcommand{\orange}[1]{\textcolor{orange}{#1}}
\newcommand{\blue}[1]{\textcolor{blue}{#1}}
\newcommand{\green}[1]{\textcolor{green}{#1}}
\newcommand{\teal}[1]{\textcolor{teal}{#1}}

% Enable this option will generate a title page containing the section name at the beginning of each section.

\AtBeginSection[]{
\begin{frame}
\vfill
\centering
\begin{beamercolorbox}[sep=8pt,center,shadow=true,rounded=true]{title}
\usebeamerfont{title}\secname\par%
\end{beamercolorbox}
\vfill
\end{frame}
}