
\documentclass[10pt]{article}
  \usepackage[utf8]{inputenc}
  \usepackage[T1]{fontenc}
  \usepackage{tcolorbox}
 
  \pagestyle{empty}

\newcommand{\pink}[1]{%
\colorbox{red!20}{#1}}

\begin{document}
Oo\pink{p}s!
\end{document}
