\usefonttheme{professionalfonts}

\RequirePackage{fontspec}

%% checkfont and iffontsavaiable copied from the metropolis theme
%% by Matthias Vo­gelge­sang.
%    Checks if a font is installed; if not, |fontsnotfound| is increased.
\newcounter{fontsnotfound}
\newcommand{\checkfont}[1]{%
  \suppressfontnotfounderror=1%
  \font\x = "#1" at 10pt
  \selectfont
  \ifx\x\nullfont%
  \stepcounter{fontsnotfound}%
  \fi%
  \suppressfontnotfounderror=0%
}
%   Resets the |fontsnotfound| counter and calls |\checkfont| for each font in
%   the comma separated list in the first argument.
\newcommand{\iffontsavailable}[3]{%
  \setcounter{fontsnotfound}{0}%
  \expandafter\forcsvlist\expandafter%
  \checkfont\expandafter{#1}%
  \ifnum\value{fontsnotfound}=0%
  #2%
  \else%
  #3%
  \fi%
}

\iffontsavailable{Libertinus Serif,%
  Libertinus Sans,%
  LibertinusMath,%
  Libertinus Mono}%
{%
  \setmainfont{Libertinus Serif}
  \setsansfont{Libertinus Sans}
  \setmathfont{Libertinus Math}
  \setmonofont{Libertinus Mono}
}{%
  \PackageWarning{beamerthememeiqss}{%
    Could not find Libertinus fonts.
    Please install them from
    https://github.com/libertinus-fonts/libertinus/releases
    following the instructions at
    https://github.com/IQSS/iqss-beamer-theme/blob/master/README.md% 
  }
}