Vertical coloured title with mdframed

Question

I'm trying without sucess to make an environment like this:

What I have know is this:

The perfect answer to this question would be a way to have the title in colors and text out of the mdframed environment. The reason of this is because if you have to many text (or larges equations), mdframed goes crazy with "overfull \vbox". Part of my code is this:

\documentclass[a4paper, 12pt]{article}


\usepackage[framemethod=TikZ]{mdframed}
\newcounter{solution}[section]
\renewcommand{\thesolution}{\arabic{section}.\arabic{solution}}

\newenvironment{solution}[1][]{%
    \refstepcounter{solution}

    % Always:
    \mdfsetup{leftmargin = 0.25cm, rightmargin = 0cm,
        innertopmargin = 0.25cm, linecolor = gray!50,
        linewidth = 2pt, topline = true, 
        frametitleaboveskip = \dimexpr-\ht\strutbox\relax}

    % 'if' condition (without title)
    \ifstrempty{#1}%
        {\mdfsetup{frametitle = {%
            \tikz[baseline = (current bounding box.east), 
            outer sep = 0pt]
            \node[anchor = east, rectangle, fill = gray!50]
            {\strut Soluci\'on};}}
        }
    % 'else' condition (with title)
        {\mdfsetup{frametitle = {%
            \tikz[baseline = (current bounding box.east), 
            outer sep = 0pt]
            \node[anchor = east, rectangle, fill= gray!50]
            {\strut Soluci\'on: #1};}}
        }
    
        
    \begin{mdframed}[]\relax}{%
    \end{mdframed}}

By the way, what I mean with "goes crazy" is this:

Thanks for read!

Answer 1

As Ulrike suggested, it can be easily done with tcolorbox:

\documentclass[a4paper, 12pt]{article}
\usepackage{mwe}%for testing purpose only
\usepackage{tcolorbox}
\tcbuselibrary{skins, breakable}
\newtcolorbox{solution}[2][]{%
enhanced,breakable,
attach boxed title to top left,
left = 0.25cm, right = 0cm,
%frame hidden,
title={\strut Soluci\'on: #2},
colbacktitle=gray!50,
coltitle=black,fonttitle=\bfseries,
attach boxed title to top left={yshift=-\tcboxedtitleheight/2, xshift=4mm},
boxed title style={sharp corners,colframe=gray!50, boxsep=0pt},
top=\tcboxedtitleheight/2+2mm,
opacityframe=0, opacityback=0,
borderline horizontal={0.5mm}{0pt}{gray!50},
}
\begin{document}
\begin{solution}{Title of the solution}
Something something 
\end{solution}
\begin{solution}{Another solution}
It is also breakable

For testing purpose only: \blindtext[4]
\end{solution}
\end{document}

Edit:
Using a default title if the title is empty:

\documentclass[a4paper, 12pt]{article}
\usepackage{mwe}%for testing purpose only
\usepackage{etoolbox}
\usepackage{tcolorbox}
\tcbuselibrary{skins, breakable}
\newtcolorbox{solution}[2][]{%
enhanced,breakable,
attach boxed title to top left,
left = 0.25cm, right = 0cm,
%frame hidden,
title={\strut Soluci\'on: \ifstrempty{#2}{Default title}{#2}},
colbacktitle=gray!50,
coltitle=black,fonttitle=\bfseries,
attach boxed title to top left={yshift=-\tcboxedtitleheight/2, xshift=4mm},
boxed title style={sharp corners,colframe=gray!50, boxsep=0pt},
top=\tcboxedtitleheight/2+2mm,
opacityframe=0, opacityback=0,
borderline horizontal={0.5mm}{0pt}{gray!50},
}
\begin{document}
\begin{solution}{Title of the solution}
Something something 
\end{solution}
\begin{solution}{}
Something something 
\end{solution}
\begin{solution}{Another solution}
It is also breakable

For testing purpose only: \blindtext[4]
\end{solution}
\end{document}