documentclass{beamer}
usepackage{lmodern}
usepackage[most]{tcolorbox}

tcbset{beamer,colback=blue!20!white,colframe=blue!75!black}

begin{document}
begin{frame}{Some boxes}
begin{tcolorbox}[title=Title]
block text
end{tcolorbox}

begin{tcolorbox}[title=Title,boxsep=3mm]
block text
end{tcolorbox}

begin{tcolorbox}[title=Title, size=small]
block text
end{tcolorbox}

begin{tcolorbox}[title=Title, width=4cm,size=fbox]
block text
end{tcolorbox}
end{frame}
end{document}