documentclass{article}
usepackage{tikz, adjustbox}
usepackage[most]{tcolorbox}

begin{document}

begin{centering}
tcbset{colback=blue!5!white,colframe=blue!75!black,fonttitle=bfseries, width = 6cm}
begin{tcolorbox}[title = First box,before=adjustbox{valign=t}bgroup, after=egroup]
begin{itemize}
item A
item B
item C
item D
item E
end{itemize}
end{tcolorbox}
tcbset{colback=red!5!white,colframe=red!75!black,fonttitle=bfseries, width = 5cm}
begin{tcolorbox}[title = Second box,before=adjustbox{valign=t}bgroup, after=egroup]
begin{itemize}
item F
end{itemize}
end{tcolorbox}
tcbset{colback=green!5!white,colframe=green!75!black,fonttitle=bfseries, width = 5cm}
begin{tcolorbox}[title = Third box]
begin{itemize}
item G
item H
item I
item J
end{itemize}
end{tcolorbox}

end{centering}

end{document}