documentclass{article}
usepackage[utf8]{inputenc}
usepackage{tcolorbox}
tcbuselibrary{skins}
usetikzlibrary{shadows}


begin{document}
begin{tcolorbox}[enhanced,width=2.5cm,
square,circular arc,
halign=center,valign=center,
colback=red!5!white,colframe=red!75!black,
frame style={circular glow={fill=red}} ]
tcolorbox
end{tcolorbox}


end{document}

shadow scale=1.25, shadow xshift=0pt, shadow yshift=0pt,
fill=black, path fading={circle with fuzzy edge 15 percent},
every shadow,