How to create theorem boxes

Question

I wrote a chapter for a book, and we use a structure.tex with a lot of definitios and macros. Now I'm writing other book and I would like to use those kind of boxes as below.

Note that when the box can't be in a single page, it divides in two and the box is not closed in the first page. Basically are two tipes of boxes.

I have the structure.tex. I tried to write a new .tex but there are a lot of errors and I have been all day trying make it work. There are various packages I can't understant. structure.tex

How can I define those things as \begin{name}.. \end{name} ?

Answer 1

This can be quite easily achieved with tcolorbox:

\documentclass{article}
\usepackage{amsmath}
\usepackage{cleveref}
\usepackage[most]{tcolorbox}
\newtcbtheorem{Theorem}{Theorem}{
  enhanced,
  sharp corners,
  attach boxed title to top left={
    yshifttext=-1mm
  },
  colback=white,
  colframe=blue!75!black,
  fonttitle=\bfseries,
  boxed title style={
    sharp corners,
    size=small,
    colback=blue!75!black,
    colframe=blue!75!black,
  } 
}{thm}
\newtcbtheorem[no counter]{Proof}{Proof}{
  enhanced,
  sharp corners,
  attach boxed title to top left={
    yshifttext=-1mm
  },
  colback=white,
  colframe=blue!25,
  fonttitle=\bfseries,
  coltitle=black,
  boxed title style={
    sharp corners,
    size=small,
    colback=blue!25,
    colframe=blue!25,
  } 
}{prf}

\begin{document}
\begin{Theorem}{}{fermat}
  No three positive integers \(a\), \(b\) and \(c\) satisfy the equation \(a^{n}
  + b^{n} = c^{n}\) for any integer greater than two.
\end{Theorem}
\begin{Proof}{Theorem \ref{thm:fermat}}{}
  The proof is easy, but too large to fit in this box.
\end{Proof}
\end{document}

Have a read in its documentation for what each setting does (I will admit, the defaults are a little annoying, hence why there are so many options). It also supports breaking boxes across pages!