How can I create boxes like the frametitle and framesubtitle in the middle of a frame?

Question

I am preparing a lecture note in beamer. I want to make headings in the middle of the frame which should look like frametitle or framesubtitle boxes. In the following MWE, I am using a block to create it, but I want the block body to be empty. How do I achieve this?

\documentclass[aspectratio=169,10pt, notheorems]{beamer}
\usefonttheme{serif}
\usetheme{CambridgeUS}
\usepackage{xcolor}
\setbeamercolor{background canvas}{bg=black}
\setbeamercolor{normal text}{fg=white}
\setbeamercolor{structure}{fg=magenta}
\setbeamercolor{structure}{bg=black}
\begin{document}
    \begin{frame}{Frame title}{Frame subtitle}
        Proof of a theorem ends here. Title heading for the next section should appear in the following box.
        \begin{block}{This box should look like frame title box}
        \end{block}
        Title heading for the next subsection should appear in the following box.
        \begin{block}{This box should look like frame subtitle box}
        \end{block}
    \end{frame}
\end{document}

PS: This answer did not help.

Answer 1

You can lookup the definition by searching where your frametitle template gets defined. For the theme CambridgeUS you will find, that it uses beamerouterthemedefault.sty and hence you can borrow the definition of the beamercolorbox from there and strip it of everything that is only used in the special purpose of a frametitle. Then you can easily use it in your MWE like this:

\documentclass[aspectratio=169,10pt, notheorems]{beamer}
\usefonttheme{serif}
\usetheme{CambridgeUS}
\usepackage{xcolor}
\setbeamercolor{background canvas}{bg=black}
\setbeamercolor{normal text}{fg=white}
\setbeamercolor{structure}{fg=magenta}
\setbeamercolor{structure}{bg=black}
\begin{document}
\begin{frame}{Frame title}{Frame subtitle}
    Proof of a theorem ends here. Title heading for the next section should appear in the following box.
\begin{beamercolorbox}[sep=0.3cm,left,wd=\textwidth]{frametitle}
    \usebeamerfont{frametitle}%
    \vbox{}\vskip-1ex%
    \strut This box should look like frame title box \strut\par%
    {\usebeamerfont{framesubtitle}\usebeamercolor[fg]{framesubtitle}This box should look like frame subtitle box\strut\par}%
    \vskip-1ex%
\end{beamercolorbox}%
\end{frame}
\end{document}

which results in:

---

If you want a box of full paper width and with the text split in two parts, here we go:

\documentclass[aspectratio=169,10pt, notheorems]{beamer}
\usefonttheme{serif}
\usetheme{CambridgeUS}
\usepackage{xcolor}
\setbeamercolor{background canvas}{bg=black}
\setbeamercolor{normal text}{fg=white}
\setbeamercolor{structure}{fg=magenta}
\setbeamercolor{structure}{bg=black}
\begin{document}
\begin{frame}{Frame title}{Frame subtitle}
    Proof of a theorem ends here. Title heading for the next section should appear in the following box.
\begin{beamercolorbox}[sep=0.3cm,left,wd=\paperwidth]{frametitle}
    \usebeamerfont{frametitle}%
    \vbox{}\vskip-1ex%
    \strut This box should look like frame title box \strut\par%
    \vskip-1ex%
\end{beamercolorbox}%
\begin{beamercolorbox}[sep=0.3cm,left,wd=\paperwidth]{frametitle}
    {\usebeamerfont{framesubtitle}\usebeamercolor[fg]{framesubtitle}This box should look like frame subtitle box\strut\par}%
    \vskip-1ex%
\end{beamercolorbox}%
\end{frame}
\end{document}