LaTeX Forum

\documentclass[a4paper, 12pt]{scrbook}

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Fancy box mit mdframed package 
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\usepackage[framemethod=TikZ]{mdframed}
\newcounter{theo}[section]\setcounter{theo}{0}
\renewcommand{\thetheo}{\arabic{section}.\arabic{theo}}
\newenvironment{theo}[2][]{%
\refstepcounter{theo}%
\ifstrempty{#1}%
{\mdfsetup{%
frametitle={%
\tikz[baseline=(current bounding box.east),outer sep=0pt]
\node[anchor=east,rectangle,fill=blue!20]
{\strut Theorem~\thetheo};}}
}%
{\mdfsetup{%
frametitle={%
\tikz[baseline=(current bounding box.east),outer sep=0pt]
\node[anchor=east,rectangle,fill=blue!20]
{\strut Theorem~\thetheo:~#1};}}%
}%
\mdfsetup{innertopmargin=10pt,linecolor=blue!20,%
linewidth=2pt,topline=true,%
frametitleaboveskip=\dimexpr-\ht\strutbox\relax
}
\begin{mdframed}[]\relax%
\label{#2}}{\end{mdframed}}

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\begin{document}

\begin{theo}[Pythagoras' theorem]{thm:pythagoras}
Hier soll die zentrale Forschungsfrage stehen. Im Box Header soll auf keine Section verwiesen bzw. manuell "Zentrale Forschungsfrage" ergaenzt werden. 
\end{theo}

\end{document}

\documentclass[fontsize=12pt]{scrbook}
\usepackage[utf8]{inputenc}% darf bei einer aktuellen TeX-Distribution entfallen
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage[ngerman]{babel}
\usepackage{csquotes}
\usepackage{tcolorbox}

\begin{document}
\begin{tcolorbox}[title=Zentrale Forschungsfrage]
Hier soll die zentrale Forschungsfrage stehen. Im Box Header soll auf keine Section verwiesen bzw. manuell \enquote{Zentrale Forschungsfrage} ergänzt werden. 
\end{tcolorbox}
\end{document}