用tcolorbox设计一个漂亮的章节样式

代码如下：

\documentclass{book}
\usepackage[explicit]{titlesec}
\usepackage[many]{tcolorbox}
\usepackage{lmodern}
\usepackage{lipsum}

\definecolor{titlebgdark}{RGB}{0,163,243}
\definecolor{titlebglight}{RGB}{191,233,251}

\titleformat{\chapter}[display]
 {\normalfont\huge\bfseries}
 {}
 {20pt}
 {%
 \begin{tcolorbox}[
 enhanced,
 colback=titlebgdark,
 boxrule=0.25cm,
 colframe=titlebglight,
 arc=0pt,
 outer arc=0pt,
 leftrule=0pt,
 rightrule=0pt,
 fontupper=\color{white}\sffamily\bfseries\huge,
 enlarge left by=-1in-\hoffset-\oddsidemargin,
 enlarge right by=-\paperwidth+1in+\hoffset+\oddsidemargin+\textwidth,
 width=\paperwidth,
 left=1in+\hoffset+\oddsidemargin,
 right=\paperwidth-1in-\hoffset-\oddsidemargin-\textwidth,
 top=0.6cm,
 bottom=0.6cm,
 overlay={
 \node[
 fill=titlebgdark,
 draw=titlebglight,
 line width=0.15cm,
 inner sep=0pt,
 text width=1.7cm,
 minimum height=1.7cm,
 align=center,
 font=\color{white}\sffamily\bfseries\fontsize{30}{36}\selectfont
 ]
 (chapname)
 at ([xshift=-4cm]frame.north east)
 {\thechapter};
 \node[font=\small,anchor=south,inner sep=2pt] at (chapname.north)
 {\MakeUppercase\chaptertitlename};
 }
 ]
 #1
 \end{tcolorbox}%
 }
\titleformat{name=\chapter,numberless}[display]
 {\normalfont\huge\bfseries}
 {}
 {20pt}
 {%
 \begin{tcolorbox}[
 enhanced,
 colback=titlebgdark,
 boxrule=0.25cm,
 colframe=titlebglight,
 arc=0pt,
 outer arc=0pt,
 remember as=title,
 leftrule=0pt,
 rightrule=0pt,
 fontupper=\color{white}\sffamily\bfseries\huge,
 enlarge left by=-1in-\hoffset-\oddsidemargin,
 enlarge right by=-\paperwidth+1in+\hoffset+\oddsidemargin+\textwidth,
 width=\paperwidth,
 left=1in+\hoffset+\oddsidemargin,
 right=\paperwidth-1in-\hoffset-\oddsidemargin-\textwidth,
 top=0.6cm,
 bottom=0.6cm,
 ]
 #1
 \end{tcolorbox}%
 }
\titlespacing*{\chapter}
 {0pt}{0pt}{40pt}
\makeatother

\begin{document}

\chapter*{A test unnumbered chapter}
\lipsum[4]
\chapter{A test chapter with a long title that will span more than one line}
\lipsum[4]

\end{document}

选自：http://tex.stackexchange.com/questions/254318/chapter-style-with-tcolorbox