\newtcbtheorem 段落开头消隐

Question

我在 Beamer 上使用该软件包\newtcbtheorem。由于某种原因，段落的第一个字母变白了。知道发生了什么吗？

\documentclass[xcolor,10pt]{beamer} 

\usetheme{metropolis}

\usepackage{tcolorbox}
\tcbuselibrary{theorems}

%%%Environments
\newtcbtheorem{mydef}{Definition}%
{colback=white,
colframe=red!35!white,
enhanced,
  sharp corners,
fonttitle=\bfseries
}{th}


\begin{document}

%------------------------------------------------------
\begin{frame}{Definitions and notation}
\begin{mydef}{Teste}
The first letter, which is T. is missing.
\end{mydef}
\end{frame}

\end{document}