Nicematrix Package: I Want the First Row and the First Column of the Table Boldfaced

Question

I want the first row and the first column boldfaced The use of the package nicematrix in my document because of my previous table style in this answer

\documentclass[10pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{graphicx, float}
\usepackage{nicematrix}
\begin{document}
    \begin{table}[H]
    \centering
    \footnotesize
    \caption{What I Model for AR(2) at $n=10$}
    \label{tabb1}
    \resizebox{\textwidth}{7em}{%
        \begin{NiceTabular}{|c|c|c|c|}
            \hline
            \RowStyle{\bfseries}
            \textbf{} &
            \textbf{$\phi = (.4, .4)$} &
            \textbf{$\phi = (.45, .45)$} &
            \textbf{$\phi = (.35, .6)$} \\ \hline
            \textit{\textbf{$sd = 1$}} &
            $X_{t} = 0.0 + 0.4X_{t-1} + 0.4X_{t-2}; \varepsilon_{t} \sim  N(0,\,1)$ &
            $X_{t} = 0.0 + 0.45X_{t-1} + 0.45X_{t-2}; \varepsilon_{t} \sim  N(0,\,1)$ &
            $X_{t} = 0.0 + 0.35X_{t-1} + 0.6X_{t-2}; \varepsilon_{t} \sim  N(0,\,1)$ \\ \hline
            \textit{\textbf{$sd = 3$}} &
            $X_{t} = 0.0 + 0.4X_{t-1} + 0.4X_{t-2}; \varepsilon_{t} \sim  N(0,\,3)$ &
            $X_{t} = 0.0 + 0.45X_{t-1} + 0.45X_{t-2}; \varepsilon_{t} \sim  N(0,\,3)$ &
            $X_{t} = 0.0 + 0.35X_{t-1} + 0.6X_{t-2}; \varepsilon_{t} \sim  N(0,\,3)$ \\ \hline
            \textit{\textbf{$sd = 5$}} &
            $X_{t} = 0.0 + 0.4X_{t-1} + 0.4X_{t-2}; \varepsilon_{t} \sim  N(0,\,5)$ &
            $X_{t} = 0.0 + 0.45X_{t-1} + 0.45X_{t-2}; \varepsilon_{t} \sim  N(0,\,5)$ &
            $X_{t} = 0.0 + 0.35X_{t-1} + 0.6X_{t-2}; \varepsilon_{t} \sim  N(0,\,5)$ \\ \hline
            \textit{\textbf{$sd = 10$}} &
            $X_{t} = 0.0 + 0.4X_{t-1} + 0.4X_{t-2}; \varepsilon_{t} \sim  N(0,\,10)$ &
            $X_{t} = 0.0 + 0.45X_{t-1} + 0.45X_{t-2}; \varepsilon_{t} \sim  N(0,\,10)$ &
            $X_{t} = 0.0 + 0.35X_{t-1} + 0.6X_{t-2}; \varepsilon_{t} \sim  N(0,\,10)$ \\ \hline
            \end{NiceTabular}
        }
    \end{table}
\end{document}

Here is the of this code but I want the first row and first column to be boldfaced.