the simple way

by changing muse-html.el, in this file, there is a default header for every page

more flexiable way

refer to Quickstart.muse

pet@girl:~$ cp  lisp-lib/muse_peter/examples/mwolson/templates/  .emacs.d/muse

pet@girl:~$ cp  lisp-lib/muse_peter/examples/mwolson/stylesheets/peter.css /home/pet/

trap

when you modify sth, be sure to run this if you want to see the modification

M-x muse-project-delete-output-files

and if you modify .el file, you need to restart emacs.