\documentclass{beamer}
\usetheme{Frankfurt}
\usecolortheme{seahorse}
\usepackage[utf8]{inputenc}

\begin{document}

\begin{frame}
	\frametitle{Lemon sorbet}
	\framesubtitle{Incarnation of good?}
	\begin{definition}
		A lemon sorbet is a
		semi-frozen \textbf{dessert}
		on \textit{lemon} base.
	\end{definition}
\end{frame}

\end{document}