How to access to the exact value of the vertical space before and after a theorem?

Question

Background

I'm using a theorem style where there is a new line between the title and the statement.

\newtheoremstyle{simple}
{}{}
{\normalfont}{}
{\normalfont}{}
{\newline}
{{\thmname{#1}\nobreakspace\thmnumber{#2}}
  {\thmnote{\hspace{.4em}\ensuremath{(\text{#3})}}}\smallskip}

To effectively prevent page break following the title, I decided to put it inside a transparent tcolorbox where one can use the key breakable and set lines before break = 3. (The reason that I chose to adopt this complicated method is that those "normal" solutions I've found, like in this question, does not work quite well.)

I have succeeded in producing such a box and wrapping the environment within it. However, I was not able to reproduce the exact vertical spaces before and after a theorem. My guessed value was \topsep+\parskip, which is smaller than the actual value (I also tried e.g. \thm@preskip and \thm@postskip, but they seem to be 0pt).

Is there some way to access to the exact value of these vertical spaces?

(The goal is to produce the same result, except for page breaking point, with or without the extra tcolorbox.)

---

Note: the question actually has little to do with tcolorbox. The thing I'm interested is the exact value of these two lengths:

---

Below is a MWE. You can comment and uncomment the ExplSyntax part (which wraps a tcolorbox around the environment theorem) to see the difference.

\documentclass{article}
\usepackage{geometry}
\usepackage{amsthm}
\newtheoremstyle{simple}
{}{}
{\normalfont}{}
{\normalfont}{}
{\newline}
{{\thmname{#1}\nobreakspace\thmnumber{#2}}
  {\thmnote{\hspace{.4em}\ensuremath{(\text{#3})}}}\smallskip}
\theoremstyle{simple}
\newtheorem{theorem}{Theorem}
\ExplSyntaxOn
\PassOptionsToPackage { many } { tcolorbox }
\RequirePackage { tcolorbox }
\cs_new_protected:Nn \minimclass_box_environment:n
  {
    \hook_gput_code:nnn { env/#1/before } { minimalist }
      {
        \begin { tcolorbox }
          [
            enhanced~jigsaw,
            frame~hidden,
            interior~hidden,
            top = 0pt, bottom = 0pt,
            left = 0pt, right = 0pt,
            boxrule = 0pt, boxsep = 0pt,
            before~skip = \topsep+\parskip,
            after~skip = \topsep+\parskip,
            breakable, lines~before~break=3,
          ]
      }
    \hook_gput_code:nnn { env/#1/after } { minimalist }
      {
        \end { tcolorbox }
      }
  }
\minimclass_box_environment:n { theorem }
\ExplSyntaxOff
\usepackage{blindtext}
\begin{document}
\blindtext
\begin{theorem}
  \blindtext
\end{theorem}
\blindtext
\begin{theorem}
  \blindtext
\end{theorem}
\begin{proof}
  \blindtext
\end{proof}
\end{document}