\begin 与其定义不符

Question

我尝试创建一个带有文本的透明框。因此，我创建了一个名为 mybox 的新颜色框。

\usepackage[many]{tcolorbox}
\usepackage{lmodern}    % just to avoid font size warnings

\newtcolorbox{mybox}[1][]{
    width=20cm,
    arc=3mm,
%    auto outer arc,
    boxsep=0cm,
    coltext = white,
    colback = black,
    toprule=0pt,
    leftrule=0pt,
    bottomrule=0pt,
    rightrule=0pt,
    colframe=black,
    fontupper=\centering\fontsize{26pt}{26pt}\itshape,
    breakable,
    nobeforeafter,
    enhanced jigsaw,
    opacityframe=0.8,
    opacityback=0.8
}

然后我尝试插入下面提到的文本。但我收到一条错误消息\begin doesn't match its definition。我找不到原因。有人能找到原因吗？注意：尽管出现了该错误，但框已创建，但我无法将文本设为粗体。

\title{
\begin{mybox}[]
 \textbf{Voltage Regulation on a High PV penetrated Distributed System using Electric Vehicles}
\end{mybox}
  }