Center block on frame with Beamer

Question

I wanted to change the block width in my presentations so, after a quick search on the website, I found the varblock solution : Changing default width of blocks in beamer

It consists in adding :

\newenvironment<>{varblock}[2][.9\textwidth]{%
  \setlength{\textwidth}{#1}
  \begin{actionenv}#3%
    \def\insertblocktitle{#2}%
    \par%
    \usebeamertemplate{block begin}}
  {\par%
    \usebeamertemplate{block end}%
  \end{actionenv}}

to the preamble. Now, in my .tex document, I have blocks like this :

\begin{varblock}[8cm]{Title}
Some content...
\end{varblock}

But I cannot center the block horizontally on the frame. I tried to put these three lines between \begin{center}...\end{center} and \begin{centering}...\end{centering} but the block still remains on the left side of the frame. Thanks for your help.

Answer 1

If the shortened block is put inside a minipage, you can center it easily

\documentclass{beamer}
\usetheme{Warsaw}

\newenvironment<>{varblock}[2][.9\textwidth]{%
    \begin{minipage}{#1}
    \begin{actionenv}#3%
        \def\insertblocktitle{#2}%
        \par%
        \usebeamertemplate{block begin}}
    {\par%
        \usebeamertemplate{block end}%
    \end{actionenv}
    \end{minipage}}
    
\begin{document}
    \begin{frame}
        \begin{center}
                \begin{varblock}[4cm]{New block}
                    Variable width, here 4cm
                \end{varblock}
        \end{center}
    \end{frame}
\end{document}

---

Another possibility is to use the tcolorbox inner beamer theme and then redefine your varblock using a tcolorbox:

\documentclass{beamer}
\usetheme{Warsaw}

\useinnertheme{tcolorbox}
\newtcolorbox{varblock}[2][.9\textwidth]{width=#1,title=#2,center}

\begin{document}
    \begin{frame}
                \begin{varblock}[4cm]{New block}
                    Variable width, here 4cm
                \end{varblock}
    \end{frame}
\end{document}

Answer 2

If you use minipage as indicated by samcarter, you can use block and omit the varblock definition since minipage already allows for reducing the width of the block:

\documentclass{beamer}
\usetheme{Warsaw}

\begin{document}
    \begin{frame}
        \begin{center}
            \begin{minipage}{4cm}
                \begin{block}{New block}
                    Variable width, here 4cm
                \end{block}
            \end{minipage}
        \end{center}
    \end{frame}
\end{document}

Answer 3

It might be related to my theme, but the minipage environment is messing with the space between the block header and block body. Putting it in columns solved this issue for me:

\documentclass{beamer}
\usetheme{Warsaw}

\begin{document}
  \begin{frame}
    \begin{columns}[T]
      \column{0.25\textwidth}
      \column{0.5\textwidth}
      \begin{block}{New block}
         Variable width, here 50%
      \end{block}
    \column{0.25\textwidth}
    \end{columns}
  \end{frame}
\end{document}