I have seen this:
Formatting headers in the book class
And I want what the asker has in their question:
\documentclass[10pt]{book}
\usepackage{blindtext}
\usepackage[a4paper]{geometry}
\usepackage{fancyhdr}
\fancyhead[LE,RO]{\thepage}
\fancyfoot{}
\cfoot{} % get rid of the page number
\pagestyle{fancy}
\begin{document}
\blinddocument
\end{document}
I am able to run this MWE. However, I have a modular document: I input other .tex files and compile everything together into one document.
For example, I have (thesis.tex):
\documentclass[letterpaper,12pt,titlepage,openright,twoside,final]{book}
\usepackage[flushleft]{threeparttable}
\usepackage{amsfonts}
\usepackage{fancyhdr}
\usepackage{mathtools,dcolumn,epsfig,rotating,bm}
\usepackage[utf8]{inputenc} %just added
\setlength{\marginparwidth}{0pt} % width of margin notes
\setlength{\marginparsep}{0pt} % width of space between body text and margin notes
\setlength{\evensidemargin}{0.125in} % Adds 1/8 in. to binding side of all
\setlength{\oddsidemargin}{0.125in} % Adds 1/8 in. to the left of all pages
\setlength{\textwidth}{6.375in} % assuming US letter paper (8.5 in. x 11 in.) and
% side margins as above
\raggedbottom
%\fancyhead[LE,RO]{\thepage}
%\cfoot{}
%\pagestyle{fancy}
\begin{document}
\input{document1.tex}
\input{document2.tex}
\end{document}
For ease of replication, suppose document1.tex is:
% !TeX root = thesis.tex
\chapter{}
Text is here in chapter 1.
and document2.tex is:
% !TeX root = thesis.tex
\chapter{}
Text is here in chapter 2.
But I can't get the header to be inside the margin. That is, I want "CHAPTER 1" and all other headers to be within the upper margin area, instead of inside the text area.
EDIT: Maybe it's easier to ask: how do I put the header higher up on the page?
Any ideas on how I can do that?