newenvironment behaving differently inside another environment

Question

Friends,

Please have a look at the code below. The problem is the environment hlcard is behaving differently when it is inside card environment, or directly under frame. I have picked the card environment directly from net, and doesn't have much clue what those long optional argument is doing. Kindly help.

The behaivour directly inside frame is the expected behaviour

\documentclass[12pt]{beamer}
\usepackage[customcolors,shade]{hf-tikz}
\usetikzlibrary{arrows,shadows,petri,decorations.markings,shapes}
\RequirePackage[many]{tcolorbox}
\definecolor{dcol}{HTML}{3F51B5}
\definecolor{BGgrey03}{RGB}{190,190,190}
\definecolor{BGgrey04}{RGB}{230,230,230}
\usecolortheme[named=dcol]{structure}
\usepackage{biblatex}

\tcbset{%
colback=BGgrey04, colbacktitle=dcol, coltitle=white, coltext=dcol,%
enhanced, sharpish corners=all,%
fuzzy shadow={0mm}{0.9mm}{0.6mm}{0.2mm}{black!20!BGgrey03}, % top
fuzzy shadow={0mm}{-0.6mm}{-0.1mm}{0.2mm}{black!40!BGgrey03}, % bottomSmall
fuzzy shadow={0mm}{-0.2mm}{-0.2mm}{0.2mm}{black!20!BGgrey03}, % bottomBig
left=6mm, right=6mm, top=6mm, bottom=6mm, middle=4mm,%
title filled, boxrule=0mm, %
segmentation code={\path[draw=BGgrey01](segmentation.west) -- (segmentation.east);}%
}

\newenvironment{card}[1][pR23s2OTKY]{%
    \ifthenelse{\equal{#1}{pR23s2OTKY}}{%
      \begin{tcolorbox}%
    }{%
      \begin{tcolorbox}[colbacktitle=dcol, coltitle=white, title=#1, left=1mm, right=6mm, top=1mm,
        bottom=1mm, middle=4mm, toptitle=1mm, bottomtitle=1mm, ]%
    }%
}{%
  \end{tcolorbox}%
}

\newenvironment{hlcard}[1][pR23s2OTKY]{%
      \begin{tcolorbox}[noparskip, breakable, colback=dcol,%
          coltitle=black,coltext=white, fonttitle={\bfseries \scshape}, left=1mm, right=6mm, top=1mm,
        bottom=1mm, middle=4mm, toptitle=1mm, bottomtitle=1mm,]%
}{%
  \end{tcolorbox}%
}

\begin{document}
\begin{frame}
\begin{card}[Problem]
  \begin{hlcard}
    Foo
  \end{hlcard}
\end{card}
  \begin{hlcard}
    Bar
  \end{hlcard}
\end{frame}
\end{document}

Answer 1

The \tcbset macro provides for .style options, i.e. collections of specific tcolorbox (or tikz/pgfkeys), otherwise any option that is not 'wrapped' in a .style is used globally and has a side effect on tcolorbox 'layers'

Nested boxes are reset, using a default setting and the global values from tcbset.

I suggest to use an outerlayer style and an innerlayer style which calls outerlayer first, then applies its own settings.

Also the environments should be defined with \newtcolorbox instead of wrapping them in \newenvironment macros.

\documentclass[12pt]{beamer}
\usepackage[customcolors,shade]{hf-tikz}
\usetikzlibrary{arrows,shadows,petri,decorations.markings,shapes}
\RequirePackage[many]{tcolorbox}
\definecolor{dcol}{HTML}{3F51B5}
\definecolor{BGgrey03}{RGB}{190,190,190}
\definecolor{BGgrey04}{RGB}{230,230,230}
\usecolortheme[named=dcol]{structure}
\usepackage{biblatex}

% Common options
\tcbset{%
  left=6mm, right=6mm, top=6mm, bottom=6mm, middle=4mm,
}

\tcbset{
  outerlayer/.style={
    enhanced,
    sharpish corners=all,
    colbacktitle=dcol, 
    coltitle=white, 
    left=1mm, 
    right=6mm, 
    top=1mm,
    bottom=1mm, 
    middle=4mm, 
    toptitle=1mm, 
    bottomtitle=1mm,
    fuzzy shadow={0mm}{0.9mm}{0.6mm}{0.2mm}{black!20!BGgrey03}, % top
    fuzzy shadow={0mm}{-0.6mm}{-0.1mm}{0.2mm}{black!40!BGgrey03}, % bottomSmall
    fuzzy shadow={0mm}{-0.2mm}{-0.2mm}{0.2mm}{black!20!BGgrey03}, % bottomBig
    title filled, boxrule=0mm, %
    segmentation code={\path[draw=BGgrey01](segmentation.west) -- (segmentation.east);}
},
  innerlayer/.style={outerlayer,
    noparskip, 
    breakable, 
    colback=dcol,%
    coltitle=black,
    coltext=white, 
    fonttitle={\bfseries \scshape}, 
    bottomtitle=1mm}
}



\newtcolorbox{card}[1][]{%
  outerlayer,
  title=#1,
}


\newtcolorbox{hlcard}[1][]{%
  innerlayer,
  #1
}

\begin{document}
\begin{frame}
\begin{card}[Problem]
  \begin{hlcard}
    Foo
  \end{hlcard}
\end{card}
\begin{hlcard}
  Bar
\end{hlcard}
\end{frame}
\end{document}