Extra top space (an empty paragraph) if used inside tcolorbox

[muzimuzhi]

From T-F-S/tcolorbox#122. Note that theorems defined by amsthm work ok.

The problem occurs when

• \parskip is non-zero and
• tcolorbox option parbox=false is set.

\documentclass{article}
\usepackage{tcolorbox} % reproducible even prior to tcolorbox v4.32
\usepackage{lipsum}

\usepackage{amsthm}
\newtheorem{thm}{Amsthm}
\usepackage{thmtools}
\declaretheorem[name=Thmtools]{theorem}

\parskip=10pt
\def\dummy{
  Nam dui ligula, fringilla a, euismod sodales, sollicitudin vel, wisi. \par
  Morbi auctor lorem non justo. Nam lacus libero, pretium at, lobortis vitae, ultricies et, tellus.}

\begin{document}
\tcbset{parbox=false}

\begin{tcolorbox}
  \begin{theorem} \dummy \end{theorem}
\end{tcolorbox}

\begin{tcolorbox}
  \begin{thm} \dummy \end{thm}
\end{tcolorbox}
\end{document}

[mbertucci47]

The output is different now; both cases have the extra space. I think it boils down to the fact that amsthm implements theorems as trivlists, and tcolorbox produces the extra space when the box begins with a list.

\documentclass{article}
\usepackage{tcolorbox}

\parskip=10pt

\begin{document}

\begin{tcolorbox}
\begin{itemize}
\item one
\item two
\end{itemize}
\end{tcolorbox}

\tcbset{parbox=false}

\begin{tcolorbox}
\begin{itemize}
\item one
\item two
\end{itemize}
\end{tcolorbox}

\end{document}

[muzimuzhi]

Looks like (another) parbox=false problem from tcolorbox. Not sure whether the current behavior is intended.

Tested on overleaf.com, tcolorbox v4.30 (2020-04-28) won't cause empty paragraph in the parbox=false box in your example.

[mbertucci47]

I've added a comment to the corresponding closed tcolorbox issue.

[muzimuzhi]

I opened

• v5.1.0(pre2): Extra top space if parbox=false tcolorbox starts with a list T-F-S/tcolorbox#262.

[mbertucci47]

Fixed with the fix for tcolorbox #262.