\documentclass{article}
\usepackage{booktabs}
\usepackage{colortbl}

\begin{document}


\begin{tabular}{l l l}
\toprule
\rowcolor[gray]{0.7}
First       & Second      & Third       \\ \midrule
A A A A A A & B B B B B B & C C C C C C \\ \midrule
D D D D D D & E E E E E E & F F F F F F \\
\bottomrule
\end{tabular}

\vspace{1cm}

\begin{tabular}{|l |l| l|}
\toprule
First       & Second      & Third       \\ \midrule
A A A A A A & B B B B B B & C C C C C C \\ \midrule
D D D D D D & E E E E E E & F F F F F F \\
\bottomrule
\end{tabular}

\end{document}