\documentclass{book}
\usepackage{tikz}
\begin{document}
\AddToHook{shipout/background}{\put(5cm,-5cm){%
xxxx%
\begin{tikzpicture}
\shade[shading=axis,
top color=yellow,
bottom color=blue ]
(0,0) rectangle (3,3);
\end{tikzpicture}xxxx
}}
\begin{tikzpicture}
\shade[shading=axis,
top color=yellow,
bottom color=blue ]
(0,0) rectangle (1,1);
\end{tikzpicture}
\end{document}