\documentclass{article}
\usepackage{nicematrix}
\begin{document}
\begin{equation*}
    \begin{pNiceArray}{C|CC:C}[
        first-row,last-row,first-col,last-col,
        code-for-first-row=\color{blue}\scriptstyle,
        code-for-last-row=\color{blue}\scriptstyle,
        code-for-first-col=\color{blue}\scriptstyle,
        code-for-last-col=\color{blue}\scriptstyle]
            & C_1 & C_2 & C_3 & C_4 &     \\
        L_1 & 1   & 2   & 3   & 4   & L_1 \\ \hline
        L_2 & 5   & 6   & 7   & 8   & L_2 \\
        L_3 & 9   & 10  & 11  & 12  & L_3 \\ \hdottedline
        L_4 & 13  & 14  & 15  & 16  & L_4 \\
            & C_1 & C_2 & C_3 & C_4 &
    \end{pNiceArray}
\end{equation*}
\begin{equation*}
    \NiceMatrixOptions{transparent}
    \begin{pmatrix}
        1      & \cdots & \cdots & 1      \\
        0      & \ddots &        & \vdots \\
        \vdots & \ddots & \ddots & \vdots \\
        0      & \cdots & 0      & 1
    \end{pmatrix}
\end{equation*}
\end{document}