Pour l'encadrement et la centralisation du mot « Références » :
\documentclass[a4paper,12pt]{article}
\documentclass[a4paper,12pt,french]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[french]{babel}
\usepackage{sectsty}
\usepackage{framed}
\begin{document}
\section{title}
ref1 \cite{ref1}
ref2 \cite{ref2}
ref3 \cite{ref3}
ref3 \cite{ref4}
\begin{framed}
\allsectionsfont{\centering\normalfont\large\scshape}
\renewcommand\bibname{Références}
\bibliographystyle{swealpha}
\bibliographystyle{alpha-fr}
\bibliography{base_exo4}
\end{framed}
\end{document}
![alt text][1]
[1]: https://texnique.fr/osqa/upfiles/Screen_Shot_2020-11-13_at_18.24.12.pnghttps://texnique.fr/osqa/upfiles/Screen_Shot_2020-11-13_at_18.58.05.png