Thanks. This is my (source) directory structure
.
├── 404.html
├── about.markdown
├── _config.yml
├── Gemfile
├── Gemfile.lock
├── index.md
├── _posts
│ ├── A2020-03-23-welcome-to-jekyll.markdown
├── _site
│ ├── 404.html
│ ├── about
└── wx_python
├── images
│ ├── basic_frame.png
├── introduction.md
├── post01.md
├── post02.md
├── post03.md
├── post04.md
├── snippets
│ ├── basic_frame.py
└── wxpython_from_scratch.md
In my _config.yml
baseurl: "/psionman_set" # the subpath of your site, e.g. /blog
To access an image I use the code

It allows me download a snippet using the code
([raw\_frame.py](snippets/basic_frame.py))
This is at a similar place in the directory tree.
How do I need to change this?
A typical page is at https://psionman.github.io/psionman_set/wx_python/introduction.html
The menu-bar is a list of pages which it has picked up from the header in each page: typically
## WxPython from Scratch
The header is also duplicated on the displayed page
this is what it should look like