%%
%% The LaTeX Companion, 3ed
%%
%% Example 8-4-29 on page I-631 in "Poster applications".
%%
%% 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{159.0pt}


\usepackage[poster]{tcolorbox}

\tcbset{placeholder/.style={enhanced jigsaw,
  size=small,sharp corners,colframe=red!50!black,
  interior style={bottom color=red!15!white,top color=yellow!15},
  opacityback=0.5,
  underlay={\draw[red!50!black,line cap=round] (interior.south west)--(interior.north east);
    \draw[red!50!black,line cap=round] (interior.south east)--(interior.north west);},
}}%

\AddToHook{begindocument/end}{%
\begin{tcbposter}[
    poster = {columns=5,rows=4, % set up raster
      spacing=1mm,              % spacing between elements
      width=140pt,height=120pt, %  - normally not needed
      showframe},               % and show it
    boxes = {sharp corners=downhill,colframe=blue} ]}
\AddToHook{enddocument}{\end{tcbposter}}

%StartShownPreambleCommands
% Set up as in previous example
%StopShownPreambleCommands

\begin{document}
 \posterbox[colback=blue!10]
           {name=title,column=1,span=3,row=1}{}
 \posterbox{name=graphic,column=4,span=2,
            row=1,rowspan=1.5}{}
 \posterbox{name=credits,column=3,span=3,above=bottom}{}
 \posterbox{name=table,column=4,span=2,
            between=graphic and credits}{}
 \posterbox{name=T,
   sequence=1 between title and bottom then
            2 between title and bottom then
            3 between title and credits}{}
\end{document}