\documentclass[12pt,a4paper]{book}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{xcolor}
\usepackage{tikz}
\usepackage{enumitem}
\usepackage{tcolorbox}
\usepackage{lipsum}
\tcbuselibrary{vignette}
\begin{document}
\begin{itemize}[label={\begin{tikzpicture}\node[draw,fill=blue!15!white] (A) {FACT};\tcbvignette{outside node=A,raised color=blue}
\end{tikzpicture}}]
\item \lipsum[1]
\item \lipsum[1]
\end{itemize}
\end{document}