枚举中心化

Question

当我进行枚举时，我想将事物置于中心。

代码：

\documentclass[12pt]{article}
\usepackage{istgame}
\usepackage{tikz}
\usetikzlibrary{shapes,arrows.meta, positioning}
\usepackage{enumitem}
\begin{document}    
    \begin{center}
        \begin{istgame}
            \setistNewNodeStyle{max}
            [regular polygon, regular polygon sides = 3]{1.5cm}
            \setistNewNodeStyle{min}
            [regular polygon, regular polygon sides = 3, shape border rotate = 180]{1.5cm}
            \setistNewNodeStyle{chance}
            [circle]{1.2cm}
            %\xtShowTerminalNodes[box node, minimum size = 1cm]
            \def\distFactor{20};
            \xtdistance{\distFactor mm}{4*\distFactor mm}
            \setxtarrowtips[blue, thick]
            \istroot(0)[max]<center, blue>{1.5}
            \istb[blue, ->-] \istb \endist
            \xtdistance{\distFactor mm}{2*\distFactor mm}
            \istroot(1)(0-1)[chance]<center, purple>{1.5}
            \istb{0.5}[al] \istb{0.5}[ar] \endist
            \istroot(2)(0-2)[chance]<center, purple>{$-0.5$}
            \istb{0.5}[al] \istb{0.5}[ar] \endist
            \xtdistance{\distFactor mm}{\distFactor mm}
            \istroot(3)(1-1)[min]<center, red>{2}
            \istb{}{2} \istb{}{2} \endist
            \istroot(4)(1-2)[min]<center, red>{1}
            \istb{}{1} \istb{}{2} \endist
            \istroot(5)(2-1)[min]<center, red>{0}
            \istb{}{0} \istb{}{2} \endist
            \istroot(6)(2-2)[min]<center, red>{$-1$}
            \istb{}{-1} \istb{}{0} \endist
        \end{istgame}
    \end{center}
    \begin{enumerate}[leftmargin =*, label = (\alph*)]
        \item $\hphantom{a}$ \vspace{-0.75cm}\newline   
        \begin{center}
            \begin{istgame}
                \setistNewNodeStyle{max}
                [regular polygon, regular polygon sides = 3]{1.5cm}
                \setistNewNodeStyle{min}
                [regular polygon, regular polygon sides = 3, shape border rotate = 180]{1.5cm}
                \setistNewNodeStyle{chance}
                [circle]{1.2cm}
                %\xtShowTerminalNodes[box node, minimum size = 1cm]
                \def\distFactor{20};
                \xtdistance{\distFactor mm}{4*\distFactor mm}
                \setxtarrowtips[blue, thick]
                \istroot(0)[max]<center, blue>{1.5}
                \istb[blue, ->-] \istb \endist
                \xtdistance{\distFactor mm}{2*\distFactor mm}
                \istroot(1)(0-1)[chance]<center, purple>{1.5}
                \istb{0.5}[al] \istb{0.5}[ar] \endist
                \istroot(2)(0-2)[chance]<center, purple>{$-0.5$}
                \istb{0.5}[al] \istb{0.5}[ar] \endist
                \xtdistance{\distFactor mm}{\distFactor mm}
                \istroot(3)(1-1)[min]<center, red>{2}
                \istb{}{2} \istb{}{2} \endist
                \istroot(4)(1-2)[min]<center, red>{1}
                \istb{}{1} \istb{}{2} \endist
                \istroot(5)(2-1)[min]<center, red>{0}
                \istb{}{0} \istb{}{2} \endist
                \istroot(6)(2-2)[min]<center, red>{$-1$}
                \istb{}{-1} \istb{}{0} \endist
            \end{istgame}
        \end{center}
        $$a = b$$
    \end{enumerate}
    $$a = b$$
\end{document}

输出：

我意识到，每当我放置一个居中对象（例如$$ a = b $$，\begin{align*}...\end{align*}等）时，该对象始终会相对于枚举和页面右侧居中，而我实际上希望它以页面的水平中点为中心（即 x = 8.5 x 11 英寸纸张左侧 4.25 英寸）。和将enumeration居中itemize对象移动多少，如何补偿？我知道adjustwidth可以完成这项工作，只是要找到枚举将居中对象移动多少的确切值。