Unused css classes in system.diff.css

they seem not to be used anywhere indeed

I looked for these classes and couldn't find them in core. I think there might be a few more classes that aren't being used in this file:

diff-deleted
diff-changed
diff-added
diff-section-title
diff-content

This can go as well:

table.diff .even, table.diff .odd {
  background-color: inherit;
  border: none;
}

I applied #5

Reviewing this at DrupalCampNorth sprint today with @LewisNyman.
Everything seems correct except for the references to the odd and even classes don't seem to have been removed in the patch. Lewis said this references the work here #1649780: Remove first/last/odd/even classes in favor of CSS3 pseudo selectors.
I'll try to add this to the patch...

Great! Thanks for making these changes. Less CSS!

Can we get screenshots before and after of config being diffed through the UI.

Also I don't think we're using...

table.diff .diffchange {
  color: #f00;
  font-weight: bold;
}

@alexpott
After a search, I noticed that there is still a reference to .diffchange in the HWLDFWordAccumulator.php file

protected function _flushGroup($new_tag) {
    if ($this->group !== '') {
      if ($this->tag == 'mark') {
        $this->line = SafeMarkup::format('@original_line<span class="diffchange">@group</span>', ['@original_line' => $this->line, '@group' => $this->group]);
      }
      else {
        $this->line = SafeMarkup::format('@original_line@group', ['@original_line' => $this->line, '@group' => $this->group]);
      }
    }
    $this->group = '';
    $this->tag = $new_tag;
  }

Here are the screenshots :

Before :

After :

Great, thanks for adding the screenshots. Setting back to RTBC based on the comment in #16.

Committed 346567c and pushed to 8.0.x. Thanks!

Thanks for adding the beta evaluation to the issue summary.