减少 tcb 框内的空白？

Question

我如何才能减少下面 tcb 环境中证明和条目之前的空白？如能得到任何帮助我将不胜感激。

\documentclass{book}

\RequirePackage[dvipsnames]{xcolor}
\RequirePackage{geometry}
\RequirePackage{amsmath}
\RequirePackage{amssymb}
\RequirePackage{amsfonts}
\RequirePackage{amsthm}
\RequirePackage[many]{tcolorbox}
\RequirePackage{letltxmacro}
\setlength{\parskip}{4pt}

\newtcbtheorem[number within=section, list inside = theoremlist, list type = thrm]{thrm}{Theorem}%
{enhanced, breakable,
colback=r!7, colbacktitle=r!17, coltitle=RedViolet,
frame hidden, parbox=false,
arc=1.85pt, titlerule=0pt, toptitle=2pt, bottomtitle=2pt,
fonttitle=\bfseries,separator sign= : \hspace{0.005cm},
segmentation style={solid, draw=r!55, line width=1pt},
before upper=\csname @nobreakfalse\endcsname
}{th}

\newtcbtheorem[use counter from=thrm]{rmk}{Remark}%
{enhanced, breakable,
colback=ablue!13, colbacktitle=ablue!23, coltitle=Plum!90,
frame hidden, parbox=false,
arc=1.85pt, titlerule=0pt, toptitle=2pt, bottomtitle=2pt,
fonttitle=\bfseries, separator sign= : \hspace{0.005cm},
segmentation style={solid, draw=ablue!60, line width=1pt},
before upper=\csname @nobreakfalse\endcsname, halign=left
}{re}
\newtcbtheorem[use counter from=thrm]{defn}{Definition}%
{enhanced, breakable,
colback=b!7, colbacktitle=b!17, coltitle=Blue,
frame hidden, parbox=false,
arc=1.85pt, titlerule=0pt, toptitle=2pt, bottomtitle=2pt,
fonttitle=\bfseries, separator sign= : \hspace{0.005cm},
segmentation style={solid, draw=b!50, line width=1pt},
before upper=\csname @nobreakfalse\endcsname, halign=left
}{de}

\definecolor{bamboo}{rgb}{0.45,0.7,0.4}
\definecolor{mine}{rgb}{0,.4,.8}
\definecolor{b}{rgb}{0,.25,.9}
\definecolor{r}{rgb}{0.9,.3,.5}
\definecolor{ablue}{HTML}{6c31b0}
\definecolor{ared}{HTML}{C33239}
\begin{document}
\begin{defn}{Dimension, \( \dim V \) }{dim}
        \begin{itemize}
        \item The \emph{dimension} of a finite-dimensional vector space is the length of any basis of the vector space. 
        \item The dimension of \( V \) is denoted by \( \dim V \). 
    \end{itemize}
\end{defn}
    
    \begin{rmk}{Dimension of a subspace}{}
    If \( V \) is finite-dimensional and \( U \) is a subspace of \( V \), then \( \dim U \leq \dim V \).
    \tcbline 
    \begin{proof}
    dd
    \end{proof}
    
    \end{rmk}

\end{document}