\usepackage{iftex}
\ifPDFTeX
  \usepackage[$if(fontenc)$$fontenc$$else$T1$endif$]{fontenc}
  \usepackage[utf8]{inputenc}
  \usepackage{textcomp} % provide euro and other symbols
\else % if luatex or xetex
$if(mathspec)$
  \ifXeTeX
    \usepackage{mathspec} % this also loads fontspec
  \else
    \usepackage{unicode-math} % this also loads fontspec
  \fi
$else$
  \usepackage{unicode-math} % this also loads fontspec
$endif$
  \defaultfontfeatures{Scale=MatchLowercase}$-- must come before Beamer theme
  \defaultfontfeatures[\rmfamily]{Ligatures=TeX,Scale=1}
\fi
$if(fontfamily)$
$else$
$-- Set default font before Beamer theme so the theme can override it
\usepackage{lmodern}
$endif$