Beamer block - 外观有问题

Question

我制作了一个带有桌面的投影仪演示文稿，看起来像......

当我用手机打开它时，它看起来像......

\documentclass[12pt]{beamer}
\usepackage{shadowtext}
\usetheme{Warsaw} 
\setbeamercolor{section in head/foot}{fg=white,bg=black}
\setbeamercolor{subsection in head/foot}{fg=black,bg=gray!30}
\setbeamercolor{background canvas}{bg=gray!90}
\setbeamercolor{block title}{bg=purple}
\setbeamercolor{block body}{bg=gray!20}
\setbeamercolor{block title alerted}{bg=purple}        
\begin{document}
\begin{frame}
\frametitle{\shadowcolor{black}
\shadowoffset{0.8pt}
\shadowtext{%
\color{purple}Random frame
}%
}
\begin{block}{\centering 
\shadowcolor{black}
\shadowoffset{0.8pt}
\shadowtext{%
Random block
}%
}
Random text
\end{block}
\end{frame}
\end{document}

有人知道我必须改变什么吗？