\begin{table}
\centering
\begin{tblr}[         %% tabularray outer open
]                     %% tabularray outer close
{                     %% tabularray inner open
colspec={Q[]Q[]},
hline{2}={1-2}{solid, black, 0.05em},
hline{1}={1-2}{solid, black, 0.08em},
hline{5}={1-2}{solid, black, 0.08em},
row{1}={}{font=\bfseries\fontsize{0.85em}{1.15em}\selectfont},
}                     %% tabularray inner close
col_a & col_b \\
a & d \\
b & e \\
c & f \\
\end{tblr}
\end{table} 
