Given following log snippets, their explanation, and nothing else, explain what failure, if any, occurred during build of this package.

  Snippets are in a format of [X] : [Y], where [X] is a log snippet, and [Y] is the explanation.

  Snippets are delimited with '================'.

  Drawing on information from all snippets, provide a concise explanation of the issue and recommend a solution.

  Explanation of the issue, and recommended solution, should take a handful of sentences.

  Snippets:

  [HTML-Proofer found 1 failure!]: [It shows HTML-proofer ended with errors.]
=============
[- ./_site/temata/energetika.html

  *  Build error (line 778)

     No item with slug 57-doprava-ve-meste]: [It shows there was an error building the file "./_site/temata/energetika.html".]

Issue: The output file "./_site/temata/energetika.html" references an item with slug "57-doprava-ve-meste". However, no such item exists.
Resolution: Add an item with slug "57-doprava-ve-meste" or adjust the slug referenced from file "./_site/temata/energetika.html" to one that exists.
Check for typos in the slug ID.