Beamer: Imitating a beamer block - problem with the width

Question

This is a follow up on my last question. I want a text block with (text width and outer shape) the same width as a beamer block but it doesn't work. The default definitioin of a beamer block is here. They use something like \begin{beamercolorbox}[colsep*=.75ex]{block title}. But if I use this the box is not properly centered anymore.

\documentclass{beamer}
\usetheme{Berlin}

\usepackage{tikz}

\begin{document}

% as expected

\begin{frame}{Test}

\begin{block}{Test}
Test
\end{block}

\tikzstyle{myBox} = [draw=none, fill=green,
    rectangle,inner sep=10pt,align=left,minimum width=\textwidth,text width=0.8\textwidth]

\begin{centering}
\begin{tikzpicture}
\node [myBox]{dsdsadsad kdjskdj sdksdk sdks dksjkdj skdjksdjksjdksjdksjdksjdksa fjdjf dkfjdkfjdkfj kdjfkdfjkdsjfkdjf};
\end{tikzpicture}%
\end{centering}

%
\begin{block}{Test}
Test
\end{block}

\end{frame}

\end{document}

My aim is to imitate the lower part of the beamer block. I use a tikz picture because I want to change transparency and other stuff.

I would like to avoid using additional packages. Is there a way to do it with TikZ? Maybe a beamercolorbox?

Answer 1

Here is two solutions using TikZ and using the fact that a block uses an horizontal extra margin of .75ex on each side.

1st solution

Here, I enlarge the text width via a columns environment then I insert your tikzpicture using \textwidth.

\documentclass{beamer}
\usetheme{Berlin}
\usepackage{tikz}
\begin{document}
% First solution
\tikzset{myBox/.style={draw=none,fill=green,rectangle,inner sep=10pt,
    align=left,minimum width=\textwidth,text width=0.8\textwidth}}
\begin{frame}{Test}
  \begin{block}{Test}
    Test
  \end{block}
  \pgfmathsetmacro\myw{\textwidth+1.5ex}
  \begin{columns}
    \column{\myw pt}
    \begin{tikzpicture}
      \node [myBox]{dsdsadsad kdjskdj sdksdk sdks dksjkdj
        skdjksdjksjdksjdksjdksjdksa fjdjf dkfjdkfjdkfj
        kdjfkdfjkdsjfkdjf};
    \end{tikzpicture}%
  \end{columns}
  \begin{block}{Test}
    Test
  \end{block}
\end{frame}
\end{document}
\documentclass{beamer}
\usetheme{Berlin}
\usepackage{tikz}

2nd solution

Here, I use trim left and trim right to enlarge the tikzpicture beyond \textwidth and I anchor the node on the west.

\documentclass{beamer}
\usetheme{Berlin}
\usepackage{tikz}
\begin{document}
% Second solution
\tikzset{
  myPict/.style={trim left=.75ex,trim right=.75ex},
  myBox2/.style={line width=0,anchor=west,draw=none,fill=green,
    rectangle,inner sep=10pt,align=left,minimum width=\textwidth+1.5ex,
    text width=0.8*(\textwidth+1.5ex)},
}
\begin{frame}{Test2}
  \begin{block}{Test2}
    Test2
  \end{block}
  \begin{tikzpicture}[myPict]
    \node [myBox2] {dsdsadsad kdjskdj sdksdk sdks dksjkdj
      skdjksdjksjdksjdksjdksjdksa fjdjf dkfjdkfjdkfj kdjfkdfjkdsjfkdjf};
  \end{tikzpicture}
  \begin{block}{Test2}
    Test2
  \end{block}
\end{frame}
\end{document}

Answer 2

Next fragment is copied from beameruserguide:

This means that colored boxes are wider than \textwidth. Therefore, when you uses \textwidth inside TikZ box declaration, you are fixing its total width, not its exterior one.

If you want to use special boxes inside beamer I'd suggest using tcolorbox. A possible solution for your example looks like

\documentclass{beamer}
\usetheme{Berlin}

\usepackage{tikz}
\usepackage[skins,breakable]{tcolorbox}

\usepackage{lipsum}

\begin{document}

\begin{frame}{Test}

\begin{block}{Test}
dsdsadsad kdjskdj sdksdk sdks dksjkdj skdjksdjksjdksjdksjdksjdksa fjdjf dkfjdkfjdkfj kdjfkdfjkdsjfkdjf
\end{block}

\begin{centering}
\begin{tcolorbox}[enhanced, arc = 0pt, frame hidden, left=1pt, right=1pt, oversize, colback=green]
dsdsadsad kdjskdj sdksdk sdks dksjkdj skdjksdjksjdksjdksjdksjdksa fjdjf dkfjdkfjdkfj kdjfkdfjkdsjfkdjf
\end{tcolorbox}%
\end{centering}

%
\begin{block}{Test}
Test
\end{block}

\end{frame}

\end{document}