\documentclass[english,11pt,twoside,openright]{book}
\usepackage[fleqn]{amsmath} %
\usepackage{amsthm,amssymb} %
\usepackage{fancyhdr,fancyref} %
\usepackage{xcolor} %
\usepackage{colortbl} %
\usepackage[skins,theorems,most]{tcolorbox} %
\usepackage{xcolor} %
\usepackage[paperwidth=170mm,paperheight=240mm,bindingoffset=12.5mm,left=12.5mm,right=12.5mm,top=18mm,bottom=8mm,showframe,showcrop]{geometry}
\usepackage[a4,frame,cam,center]{crop} %
\usepackage{libertine} %
\usepackage{hyperref}
% \renewcommand{\chaptermark}[1]{\markboth{\fontsize{12.0}{14}\selectfont{\chaptername\hspace{2.8pt}\thechapter\hspace{8pt}-\hspace{8pt}#1}}{}} % 42
% \renewcommand{\sectionmark}[1]{\markright{\fontsize{12.0}{14}\selectfont{Section\hspace{3.6pt}\thesection\hspace{8pt}-\hspace{8pt}#1}}{}} % 32
% \fancypagestyle{mainstyle}{
% \fancyhead{} %
% \fancyfoot{} %
% \fancyhead[LE]{\leftmark} %
% \fancyhead[LO]{\rightmark} %
% \fancyfoot[CE,CO]{\fontsize{11.15}{14}\selectfont{-\hspace{2pt}{\thepage}\hspace{2pt}-}} }
\begin{document}
\chapter{The undeveloped world}
Large areas of land where population density is low.
\section[the Amazon river basin]{The Amazon river basin}
\clearpage
\section[the African river Congo]{The African river Congo}
\clearpage
\chapter{The developed world}
The population density is high.
\section[Europe - from UK in north to Spain in south]{Europe - from UK in north to Spain in south}
\clearpage
\section[North America and Canada]{North America and Canada}
\clearpage
\section[the Philippenes]{Japan and the Philippenes}
\end{document}
答案1
无需定义特定的页面样式，只需发出\pagestyle{fancy}。
此外，格式说明应在页眉或页脚的规范中，而不是在标记的说明中。
我将连字符改为短破折号：在我看来，连字符不是正确的选择（太粗且太短）。
不要忘记遵循fancyhdr有关的建议\headheight。
\documentclass[11pt,twoside,openright]{book}
\usepackage[fleqn]{amsmath}
\usepackage{amsthm,amssymb}
\usepackage{fancyhdr,fancyref}
\usepackage{xcolor}
\usepackage{colortbl}
\usepackage[skins,theorems,most]{tcolorbox}
\usepackage{xcolor}
\usepackage[
paperwidth=170mm,
paperheight=240mm,
bindingoffset=12.5mm,
left=12.5mm,
right=12.5mm,
top=18mm,
bottom=8mm,
headheight=14pt,% as requested by fancyhdr
% showframe,
% showcrop
]{geometry}
\usepackage[a4,frame,cam,center]{crop}
\usepackage{libertine}
\usepackage{hyperref}
\renewcommand{\chaptermark}[1]{%
\markboth{\chaptername\hspace{2.8pt}\thechapter\hspace{8pt}--\hspace{8pt}#1}{}%
}
\renewcommand{\sectionmark}[1]{%
\markright{Section\hspace{3.6pt}\thesection\hspace{8pt}--\hspace{8pt}#1}%
}
\pagestyle{fancy}
\fancyhf{}
\fancyhead[LE]{\fontsize{12}{14}\selectfont\leftmark}
\fancyhead[LO]{\fontsize{12.0}{14}\selectfont\rightmark}
\fancyfoot[C]{\fontsize{11.15}{14}\selectfont{--\hspace{2pt}{\thepage}\hspace{2pt}--}}
\begin{document}
\chapter{The undeveloped world}
Large areas of land where population density is low.
\section{The Amazon river basin}
\clearpage
\section{The African river Congo}
\clearpage
\chapter{The developed world}
The population density is high.
\section{Europe - from UK in north to Spain in south}
\clearpage
\section{North America and Canada}
\clearpage
\section{Japan and the Philippines}
\end{document}
答案2
您可以通过以下方式定义新标题fancyhdr's \fancypagestyle（正如你所做的那样），但这不会影响它们的使用，除非你指定它，或者更改默认值。为此，请在定义新页面样式后立即指定要使用的新页面样式：
%...
\usepackage{fancyhdr}
%...
\fancypagestyle{mainstyle}{%
% <your mainstyle page style definitions
}
%...
\pagestyle{mainstyle}% mainstyle page style in effect from here
%...
当然，请注意，\chapter只有第一页才有自己的页面样式，通常通过 发出\thispagestyle{plain}。如果您想覆盖此行为，可以定义新样式来替换plain，或重新定义plain页面样式。
根据您的具体示例，输入应该是这样的（我从您的示例中删除了一些不必要的包）：
\documentclass[twoside,openright]{book}
\usepackage{fancyhdr}
\usepackage[paperwidth=170mm,paperheight=240mm,bindingoffset=12.5mm,left=12.5mm,right=12.5mm,top=18mm,bottom=8mm,showframe,showcrop]{geometry}
\usepackage[a4,frame,cam,center]{crop}
\usepackage{libertine}
\renewcommand{\chaptermark}[1]{%
\markboth
{\fontsize{12}{14}\selectfont\chaptername\hspace{2.8pt}\thechapter\hspace{8pt}-\hspace{8pt}#1}%
{}%
} % 42
\renewcommand{\sectionmark}[1]{%
\markright
{\fontsize{12}{14}\selectfont Section\hspace{3.6pt}\thesection\hspace{8pt}-\hspace{8pt}#1}%
{}%
} % 32
% Define mainstyle page style
\fancypagestyle{mainstyle}{%
\fancyhf{}% Clear header/footer
\fancyhead[LE]{\leftmark}%
\fancyhead[LO]{\rightmark}%
\fancyfoot[CE,CO]{\fontsize{11.15}{14}\selectfont -\hspace{2pt}{\thepage}\hspace{2pt}-}%
}
\setlength{\headheight}{14pt}% Based on the size of the header content
% Set mainstyle as the current page style
\pagestyle{mainstyle}
\begin{document}
\chapter{The undeveloped world}
Large areas of land where population density is low.
\section[the Amazon river basin]{The Amazon river basin}
\clearpage
\section[the African river Congo]{The African river Congo}
\clearpage
\chapter{The developed world}
The population density is high.
\section[Europe - from UK in north to Spain in south]{Europe - from UK in north to Spain in south}
\clearpage
\section[North America and Canada]{North America and Canada}
\clearpage
\section[the Philippenes]{Japan and the Philippenes}
\end{document}