我如何获得像这样的定义和定理环境？

Question

我尝试使用该mdframed包但失败了，我该如何获得该输出？

Answer 1

可以使用“tcolorbox”包获得解决方案。有很多种可能性。我画了三种（在下面的例子中）。在第一部分中，我尝试坚持您希望的风格，为类似定理的环境设置单独的标题。

在第二部分中，构造比较简单；引理是直接使用手册中的示例获得的（几乎）。但是您没有单独的标题行。

手册第 339 页还指出了另一种可能性，即使用\newtcbtheorem，但交叉引用的标签和定义很奇怪。我个人不喜欢它。

\documentclass[11pt, a4paper]{article}
\usepackage[top=105pt, bottom=75pt, left=75pt, right=75pt]{geometry}
\setlength{\headsep}{15pt}
\setlength{\footskip}{45pt}

\usepackage{xcolor}
\usepackage{lipsum}

\usepackage{amsmath, amssymb, amsthm}
\usepackage{ifthen}
\usepackage{tikz}
\usetikzlibrary{calc}



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{tcolorbox}
\tcbuselibrary{skins, breakable}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%% with separate title
\xdefinecolor{thmTopColor}{RGB}{102, 102, 238}
\xdefinecolor{thmBackColor}{RGB}{245, 245, 255}  % white


\newenvironment{thmbox}[1]{%
  \tcolorbox[%
  empty,
  parbox=false,
  noparskip,
  enhanced,
  breakable,
  sharp corners,
  boxrule=-1pt,
  left=2ex,
  right=0ex,
  top=0ex,
  boxsep=1ex,
  before skip=2.5ex plus 2pt,
  after skip=2.5ex plus 2pt,
  colback=thmBackColor,
  colframe=white,
  coltitle=black,
  colbacktitle=thmBackColor,
  fonttitle=\bfseries,
  title=#1,
  titlerule=1pt,
  titlerule style=thmTopColor,
  overlay unbroken and last={%
    \draw[color=thmTopColor, line width=1.25pt]
    ($(frame.north west)+(.5em, -4.1ex)$)
    -- ($(frame.south west)+(.5em, 1ex)$) -- ++(2em, 0);
  }]
}{\endtcolorbox}

\newenvironment{thmb}[1][]{% before
  \refstepcounter{thm}%
  \ifthenelse{\equal{#1}{}}{%
    \begin{thmbox}{Theorem \thethm.}\itshape\hspace{-.75ex}%
  }{%
    \begin{thmbox}{Theorem \thethm%
        \hspace{.75ex}(\textnormal{#1}).}\itshape\hspace{-.75ex}
    }}
  {\end{thmbox}
}
  
  
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
%%% simple forms
% 1
\newtheorem{thm}{Theorem}[section]

\theoremstyle{definition}
\newtheorem{definition}[thm]{Definition}


\newenvironment{noticeB}[1][]{%
  \ifthenelse{\equal{#1}{}}{%
    \colorlet{cbackground}{white}
  }{\colorlet{cbackground}{#1}}
  \tcolorbox[%
  notitle,
  empty,
  enhanced,  % delete the edge of the bottom page for a broken box
  breakable,
  coltext=black,
  colback=cbackground, 
  fontupper=\rmfamily,
  parbox=false,
  noparskip,
  sharp corners,
  boxrule=-1pt,  % width of the box' edges
  frame hidden,
  left=.5\parindent,  % inner space from text to the left edge
  right=.5\parindent,
  top=5pt,
  bottom=5pt,
  % boxsep=0pt,
  before skip=2.5ex plus 2pt,
  after skip=2.5ex plus 2pt,
  borderline west = {1.5pt}{-0.1pt}{blue!30!black}, % second argument = offset
  overlay unbroken and last={%
    \draw[color=black, line width=1.25pt]
    ($(frame.south west)+(1.pt, -0.1pt)$) -- ++(2em, 0);
  }
  ]}
{\endtcolorbox}


\newenvironment{thmB}{\begin{thm}\begin{noticeB}[blue!50!black!5]}
    {\end{noticeB}\end{thm}}
\newenvironment{definitionB}{\begin{definition}\begin{noticeB}}{%
    \end{noticeB}\end{definition}}


%2
\newtheorem{lem}[thm]{Lemma}% from 'amsthm'
\tcolorboxenvironment{lem}{%
  enhanced jigsaw,
  boxrule=-1pt,
  colframe=white,
  borderline west={2pt}{0pt}{orange},  % second argument is the offset
  interior hidden,
  breakable,
  before skip=2.5ex plus 2pt,
  after skip=2.5ex plus 2pt
}

\begin{document}

\section{Based on \texttt{tcolorbox} with titles}

\begin{thmb}
  \label{th:test}
  \lipsum[5]
\end{thmb}

\lipsum[1]

\begin{thmb}[Anonymous]
  \label{th:test2}
  \lipsum[6]
\end{thmb}

Can we make a reference to Theorem \ref{th:test}?  Yes we can.



\section{With simpler definitions for the theorem-like environmants}

\begin{definitionB}
  \lipsum[1]
\end{definitionB}

\lipsum[2]

\begin{thmB}
  \lipsum[5]
\end{thmB}

\lipsum[4]

\begin{lem}[from \texttt{tcolorbox} manual]
  \lipsum[7]
\end{lem}
\end{document}