Style Kramdown's syntax highlighter line numbers.

[neizod]

First, append this into _config.yml:

kramdown:
  syntax_highlighter_opts:
    block:
      line_numbers: true

(or find other means to enable line number per code block.)

Observe that output HTML wrap <pre><code> with <table>, which now render ugly. Try to fix this issue without altering normal <table>.