在嵌套枚举环境中临时修改左边距

Question

我想在嵌套的枚举环境中插入一些没有左边距的文本块。

在下面的 MWE 中，这意味着我希望三个蓝框部分具有完整的文本宽度。

\documentclass{article}

\usepackage{xcolor}
\usepackage{mdframed}
\usepackage[shortlabels]{enumitem}


\newenvironment{answer}
{\begin{mdframed}[
  backgroundcolor   = blue!15,
  innerleftmargin   = 2mm,
  innerrightmargin  = 2mm,
  innertopmargin    = 2mm,
  needspace         = 2cm,
  topline           = false,
  bottomline        = false,
  leftline          = false,
  rightline         = false,
  nobreak           = false,
  fontcolor         = blue!70!black
  ]}
{\end{mdframed}}


% For itemize
\setlist[itemize,1]{$\bullet$, leftmargin=1.5em, labelsep=0.5em}
\setlist[itemize,2]{$\rhd$} 

% For enumerate level 1
\setlist[enumerate, 1]
{1., 
leftmargin  = 2em,
itemindent  = 0pt,
labelwidth  = 2em,
labelsep    = 0pt,
font        = \bfseries,
align       = left,
itemsep     = 1.5mm,
ref         = \mbox{\textup{\textbf{\arabic*.}}}}

% For enumerate level 2
\setlist[enumerate, 2]
{(a),
itemindent = 0pt,
labelwidth = 6.75mm,
align = left,
itemsep = 0.5mm,
leftmargin = 6.5mm,
ref=\mbox{\textup{\textbf{\theenumi{}}\hspace{1pt}(\alph*)}}}

% For enumerate level 3
\setlist[enumerate, 3]
{(i),
leftmargin = 6mm,
itemindent = 0pt,
labelsep = 1.5mm,
align = right,
itemsep = 0.25mm,
ref=\mbox{\textup{\theenumii\hspace{1pt}(\roman*)}}}


\begin{document}

\begin{enumerate}

\item
These are questions.
\begin{enumerate}

\item
These are sub questions.
\begin{enumerate}

\item
These are sub sub questions.
\begin{answer}
This is the answer.
\end{answer}
\end{enumerate}

\item This is another sub question.
\begin{answer}
This is the answer.
\end{answer}

\end{enumerate}

\item This is another question
\begin{answer}
This is the answer.
\end{answer}
\end{enumerate}

\end{document}

我希望输出更像这样：

感谢您的帮助。

Answer 1

\documentclass{article}

\usepackage{xcolor}
\usepackage{mdframed}
\usepackage[shortlabels]{enumitem}

\makeatletter
\newenvironment{answer}
{\begin{mdframed}[
  backgroundcolor   = blue!15,
  leftmargin=-\@totalleftmargin
  innerleftmargin   = 2mm,
  innerrightmargin  = 2mm,
  innertopmargin    = 2mm,
  needspace         = 2cm,
  topline           = false,
  bottomline        = false,
  leftline          = false,
  rightline         = false,
  nobreak           = false,
  fontcolor         = blue!70!black
  ]}
{\end{mdframed}}
\makeatother

% For itemize
\setlist[itemize,1]{$\bullet$, leftmargin=1.5em, labelsep=0.5em}
\setlist[itemize,2]{$\rhd$} 

% For enumerate level 1
\setlist[enumerate, 1]
{1., 
leftmargin  = 2em,
itemindent  = 0pt,
labelwidth  = 2em,
labelsep    = 0pt,
font        = \bfseries,
align       = left,
itemsep     = 1.5mm,
ref         = \mbox{\textup{\textbf{\arabic*.}}}}

% For enumerate level 2
\setlist[enumerate, 2]
{(a),
itemindent = 0pt,
labelwidth = 6.75mm,
align = left,
itemsep = 0.5mm,
leftmargin = 6.5mm,
ref=\mbox{\textup{\textbf{\theenumi{}}\hspace{1pt}(\alph*)}}}

% For enumerate level 3
\setlist[enumerate, 3]
{(i),
leftmargin = 6mm,
itemindent = 0pt,
labelsep = 1.5mm,
align = right,
itemsep = 0.25mm,
ref=\mbox{\textup{\theenumii\hspace{1pt}(\roman*)}}}




\begin{document}

\begin{enumerate}

\item
These are questions.
\begin{enumerate}

\item
These are sub questions.
\begin{enumerate}

\item
These are sub sub questions.
\begin{answer}
This is the answer.
\end{answer}
\end{enumerate}

\item This is another sub question.
\begin{answer}
This is the answer.
\end{answer}

\end{enumerate}

\item This is another question
\begin{answer}
This is the answer.
\end{answer}
\end{enumerate}

\end{document}