I need a header as the first photo, but the only thing I can do is the second photo

Question

\documentclass[twoside]{book}
\usepackage{fancyhdr}

\makeatletter
\newenvironment{tablehere}
{\def\@captype{table}}
{}
\makeatother


\fancyhead{}
\fancyhead[RO, LE]{\framebox[9\width][s]{se separan}}


\fancyfoot{}
\fancyfoot[LE, RO]{\thepage}
\fancyfoot[LO, CE]{Chapter \thechapter}

\makeatletter
\let \ps@plain\ps@fancy
\makeatother

\pagestyle{fancy}

\begin{document}
%  \input{title}

  \chapter{Introduction}
  ...

  \chapter{Background}
  ...

  \chapter{Conclusion}
  ...

  \newpage
  afjdajf
  \newpage
  sagfajg

\end{document}

Answer 1

For diagonal lines, you need TikZ. Also, fancyhdr tends to change \headheight from one page to the next, so I used \myheight instead. (TikZ draws slightly outside the bounds.) The strut is used to align the page number and "Chapter".

Needless to say, you can always adjust the position of the text relative to the tikz coordinates.

\documentclass[twoside]{book}
\usepackage{fancyhdr}
\usepackage{tikz}

\makeatletter
\newenvironment{tablehere}
{\def\@captype{table}}
{}
\makeatother

\newlength{\myheight}% fancyhdr changes \headheight from one page to the next.
\setlength{\myheight}{\dimexpr \ht\strutbox+\dp\strutbox+.666em}
\setlength{\headheight}{\dimexpr \myheight+0.5pt}% width of tikz lines

\fancyhead{}
\fancyhead[CE]{\begin{tikzpicture}
  \path[draw=black,fill=orange]  
    (0,0) -- (.7\textwidth,0) -- (.8\textwidth,\myheight) -- (0,\myheight) -- cycle;
  \path[draw=black,fill=gray]
    (.7\textwidth,0) -- (\textwidth,0) -- (\textwidth,\myheight) -- (.8\textwidth,\myheight) -- cycle;
  \path (0,0) node[above right] {\chaptername~\thechapter\strut}
    (\textwidth,0) node[above left] {\thepage\strut};
  \end{tikzpicture}}
\fancyhead[CO]{\begin{tikzpicture}\path[draw=black,fill=gray]
    (0,0) -- (.3\textwidth,0) -- (.2\textwidth,\myheight) -- (0,\myheight) -- cycle;
  \path[draw=black,fill=orange]
    (.3\textwidth,0) -- (\textwidth,0) -- (\textwidth,\myheight) -- (.2\textwidth,\myheight) -- cycle;
  \path (0,0) node[above right] {\thepage\strut}
    (\textwidth,0) node[above left] {\chaptername~\thechapter\strut};
  \end{tikzpicture}}

\makeatletter
\let \ps@plain\ps@fancy
\makeatother

\pagestyle{fancy}

\begin{document}
%  \input{title}

  \chapter{Introduction}
  ...

  \chapter{Background}
  ...

  \chapter{Conclusion}
  ...

  \newpage
  afjdajf
  \newpage
  sagfajg

\end{document}