How to put a line above the lower part of tcolorbox

Question

How can I cover the top side of the light gray part with the same line that encloses the box?

\documentclass{article}
\usepackage[many]{tcolorbox}
\usepackage{lipsum}
% --
\begin{document}
\begin{tcolorbox}[title={Title}, center title, toptitle=1mm, bottomtitle=1mm, halign lower=center, sharp corners,%
bicolor, collower=black, colback=white, colframe=black!75, colbacklower=black!50]
\lipsum[1]
\tcblower
Text
\end{tcolorbox}
\end{document}

Answer 1

A simple overlay over the segmentation node can solve the problem:

\documentclass{article}
\usepackage[many]{tcolorbox}
\usepackage{lipsum}
% --
\begin{document}
\begin{tcolorbox}[
    title={Title}, 
    center title, 
    toptitle=1mm, 
    bottomtitle=1mm, 
    halign lower=center, 
    sharp corners,%
    bicolor, 
    collower=black, 
    colback=white, 
    colframe=black!75, 
    colbacklower=black!50,
    overlay={\draw[tcbcolframe, line width=.5mm] (segmentation.west)--(segmentation.east);}]
\lipsum[1]
\tcblower
Text
\end{tcolorbox}
\end{document}

Answer 2

IN case, that your tcolorbox hasonly one color, this line you can draw by use of

segmentation engine=path,`
segmentation style={draw=black!75, line width=1.5pt, solid}

which gives:

However, when is used bicolor option, defined colors by

colbacklower=black!50,

is lost, actually it is overwritten by settings for colframe=black!75:

This I would consider as bug in package. The complete code, by which I generated bot pictures is:

\documentclass{article}
\usepackage[many]{tcolorbox}
\usepackage{lipsum}
% --
\begin{document}
\begin{tcolorbox}[enhanced,
                  title={Title}, center title, toptitle=1mm, bottomtitle=1mm,
                  halign lower=center, sharp corners,%
                  bicolor,
                  colback=white, colframe=black!75,
                  collower=white, collower=black!50,
                  segmentation engine=path,
                  segmentation style={draw=red, line width=1.5pt, solid}% red is selected that line is visible
                  ]
\lipsum[1]
\tcblower
Text
\end{tcolorbox}
\end{document}

addendum:

with plain tikz you can draw your box as follows:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{shapes.multipart}
\usepackage{lipsum}
% --
\begin{document}

\noindent%
    \begin{tikzpicture}[
mpnv/.style = {rectangle split,
    rectangle split parts=3,
    rectangle split part fill={black!75, white, black!50},
    draw=black!75, line width=1pt,
    minimum width=\linewidth, inner sep=2mm,
    text width=\linewidth-2*\pgfkeysvalueof{/pgf/inner xsep},
    align=justify
                        }%
                      ]
\node[mpnv] {\nodepart[align=center]{one}       \textcolor{white}{Text}
             \nodepart{two}                     \lipsum[1]
             \nodepart[align=center]{three}     Text
            };
    \end{tikzpicture}
\end{document}

Answer 3

Adapting the solution given by egreg to the question Issue with tabularx and hbox options in tcolorbox, it is possible to achieve the desired output.

Update (18.06.2019)

The spaces between text and frame can be set up with:

• \def\arraystretch{} for the vertical margin
• \def\tabcolsep{} for the horizontal margin

The Title can be vertically centered with the options:

• toptitle
• bottomtitle

The extra space at the bottom comes from the paragraph breaks \par after \lipsum. There are two possibilities to remove it:

• package option nopar (global option)
• starred version \lipsum* (local option)

Updated output:

Updated code:

\documentclass{article}
\usepackage{booktabs}
\usepackage{tabularx}
\usepackage{colortbl}
\usepackage{array}
\usepackage{tikz}
\usepackage{tcolorbox}
\tcbuselibrary{skins, breakable}
%\usepackage[nopar]{lipsum}
\usepackage{lipsum}

\makeatletter
\tcbset{
  tabular/.style={
    boxsep=\z@,top=\z@,bottom=\z@,leftupper=\z@,rightupper=\z@,
    toptitle=2mm,bottomtitle=2mm,boxrule=1.5pt,
    before upper={\arrayrulecolor{tcbcol@frame}\def\arraystretch{2.0}\def\tabcolsep{1.5em}%
      \tcb@hack@currenvir\tabular{#1}},
    after upper=\endtabular\arrayrulecolor{black!75}},
}
\makeatother

%--- from https://tex.stackexchange.com/a/381720/89320
%--- to remove space after \midrule
\newcommand{\midsepremove}{\aboverulesep = 0mm \belowrulesep = 0mm}
%----

\begin{document}

\midsepremove
\begin{tcolorbox}[
  skin = enhanced,
  tabular = {p{11cm}},
  capture = hbox,
%  breakable = false,
  title = {Title},
  center title,
  halign lower=center,
  sharp corners,
  colback=white,
  center,
]
    \arrayrulecolor{black!75}
    \lipsum*[1]\tabularnewline %
    \midrule[1.5pt]
    \cellcolor{black!50} \centering Text \tabularnewline
\end{tcolorbox}

\end{document}