\usepackage{tikz}
\usetikzlibrary{shapes.geometric, arrows, calc, chains, backgrounds}
\usetikzlibrary{overlay-beamer-styles}

\tikzset{
  rosbase/.style={minimum width=20mm, minimum height=7.5mm, text centered, draw=black, align=center},
  startstop/.style={rectangle, rounded corners, rosbase, fill=red!30},
  rostopic/.style={rectangle, rosbase},
  rosnode/.style={ellipse,rosbase},
  arrow/.style={thick,->,>=stealth},
}