Fix local path href in org-demo.html
Add border to <code>
Remove Stack Overflow feed in org-demo.html

I think this is causing the HTTPS/HTTP mixed content blocking in the
browser, and there's no need for an updating feed anyway.
Improve org-mode contents legibility
Fix org-mode dt font-weight
Remove span margin
Fix some link behaviour

- Fix input:hover text colour to match a:hover.

- Inherit text colour for <strong> and <em>.

- Don't inherit for org-mode keywords in links (eg. in the contents),
  because the colour improves readability a lot.