Based on the discussion here: download-a-working-local-copy-of-a-webpage, I am using following command to make download a webpage with the image:
wget --default-page -q -p -k http://mattvh.github.io/solar-theme-jekyll/index.html -O ./page_source/ex.html
For some urls this works, for others (as the one mentioned) this fails with error:
Cannot specify both -k or --convert-file-only and -O if multiple URLs are given, or in combination
with -p or -r. See the manual for details.
How to fix this?