%%
%% The LaTeX Companion, 3ed
%%
%% Example 8-4-2 on page I-615 in "tcolorbox --- The basic usage".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{207.0pt}

%StartShownPreambleCommands
\usepackage{tcolorbox}
%StopShownPreambleCommands

\begin{document}
\begin{tcolorbox}[nobeforeafter,
                  width=.45\linewidth]
   top part \tcblower bottom part
\end{tcolorbox}
\begin{tcolorbox}[nobeforeafter,sidebyside,
                  width=.45\linewidth]
   left part \tcblower right part
\end{tcolorbox}
\end{document}