xelatex (and latex/dvipdfmx) uses for fadings \pgfsys@fadingfrombox
. This means that fadings can't be used in different sizes:
\documentclass{report} \usepackage{tikz} \usetikzlibrary{fadings} \definecolor{lightGrey}{gray}{0.94} \pagestyle{empty} \begin{document} \pgfdeclarefading{fading2} {\tikz \shade[left color=pgftransparent!0, right color=pgftransparent!100] (0,0) rectangle (2,2);} \begin{tikzpicture} \fill [black!20] (0,0) rectangle (2,2); \pgfsetfading{fading2}{\pgftransformshift{\pgfpoint{1cm}{1cm}}} \fill [red] (0,0) rectangle (2,2); \end{tikzpicture} \pgfdeclarefading{fading2} {\tikz \shade[left color=pgftransparent!0, right color=pgftransparent!100] (0,0) rectangle (4,4);} \begin{tikzpicture} \fill [black!20] (0,0) rectangle (4,4); \pgfsetfading{fading2}{\pgftransformshift{\pgfpoint{2cm}{2cm}}} \fill [red] (0,0) rectangle (4,4); \end{tikzpicture} \end{document}
This means that e.g. drop shadows don't work at different sizes with xelatex. See e.g. https://tex.stackexchange.com/questions/445248/tikzpicture-blur-show-up-incorrectly/445321#445321