Link chapter-star elements properly

[#62963228]
Properly link chapter-star elements in frontmatter

[Delivers #62963228]
Issue pull request for branch chapter-toc-62963228

[Delivers #62963228](https://www.pivotaltracker.com/story/show/62963228)
[Delivers #62884836](https://www.pivotaltracker.com/story/show/62884836)
[Delivers #62884840](https://www.pivotaltracker.com/story/show/62884840)
[Delivers #62884842](https://www.pivotaltracker.com/story/show/62884842)
[Delivers #62862638](https://www.pivotaltracker.com/story/show/62862638)
[Delivers #62872772](https://www.pivotaltracker.com/story/show/62872772)
[Delivers #62802682](https://www.pivotaltracker.com/story/show/62802682)
Polish
[#62963228]

* chapter-toc-62963228:
  Polish
  Issue pull request for branch chapter-toc-62963228
  Properly link chapter-star elements in frontmatter
  Link chapter-star elements properly
  Fix an EPUB validation error
  Get custom.css working with local server
  Add support for custom.css