Put a rounded corner box in a beamer template

Question

I am trying to put a rounded corners box that contains an equation. I keep having an error: 'Missing $ inserted' and I don't understand why?

Could someone help me to figure it out please?

\documentclass{beamer}
\usepackage{fancybox}
\usepackage{amsmath}
\begin{document}
\begin{frame}
    \begin{equation}
    \ovalbox{\nabla \zeta_0 = -\frac{\delta r}{h^{}}  \ \text{avec :}\ \frac{1}{h^{}} = \frac{1}{\alpha h_p} - \frac{1}{H}}
    \end{equation}
\end{frame}
\end{document}

Answer 1

Adaptations

• the argument of \ovalbox must be in math mode

Result

Code

\documentclass{beamer}
\usepackage{fancybox}
\usepackage{amsmath}
\begin{document}
\begin{frame}
    \ovalbox{$\nabla \zeta_0 = -\frac{\delta r}{h^{}}  \ \text{avec :}\ \frac{1}{h^{}} = \frac{1}{\alpha h_p} - \frac{1}{H}$}
\end{frame}
\end{document}

Answer 2

You could use the hf-tikz package instead. This has some nice additional features, like overlay awareness, control over height and size...

Off-topic: you don't need to load amsmath, beamer loads it automatically.

\documentclass{beamer}
\usepackage[beamer,customcolors,nofill]{hf-tikz}
\hfsetbordercolor{black}
\begin{document}
\begin{frame}
    \begin{equation}
    \tikzmarkin<1->{a}(0.1,-0.4)(-0.1,0.6) 
    \nabla \zeta_0 = -\frac{\delta r}{h^{}}  \quad \text{avec :}\quad \frac{1}{h^{}} = \frac{1}{\alpha h_p} - \frac{1}{H} 
    \tikzmarkend{a}
    \end{equation}
\end{frame}
\end{document}

---

Or one could use the tcolorbox package:

\documentclass{beamer}
\usepackage[most]{tcolorbox}
\tcbset{
  every box/.style={
    highlight math style={
      colback=bg,
      colframe=black
    }
  }
}
\begin{document}
\begin{frame}
    \begin{equation}
    \tcbhighmath{
    \nabla \zeta_0 = -\frac{\delta r}{h^{}}  \quad \text{avec :}\quad \frac{1}{h^{}} = \frac{1}{\alpha h_p} - \frac{1}{H} 
    }
    \end{equation}
\end{frame}
\end{document}