Most first/last/odd/even classes removed in favor of CSS3 pseudo selectors

Summary

• 'even', 'odd', 'last', 'first' classes have been removed from most of the markup except tables
• CSS has been updated to use comparable CSS3 pseudo selectors in place of the removed class selectors

Reasoning

• Better compliance with CSS3 best practices
• Removes some markup bloat
• Removes PHP logic from theme functions and templates
• Old CSS selectors remain for tables due to issues caused by hidden table rows

Before

Example list output by theme_item_list() in Drupal 7

<ul>
  <li class="first odd">Item 1</li>
  <li class="even">Item 2</li>
  <li class="odd">Item 3</li>
  <li class="last even">Item 4</li>
</ul>

CSS to style the first, last, even, and odd elements using class selectors

li.first { . . . }
li.last { . . . }
li.even { . . . }
li.odd { . . . }

After

Example list output by theme_item_list() in Drupal 8

<ul>
  <li>Item 1</li>
  <li>Item 2</li>
  <li>Item 3</li>
  <li>Item 4</li>
</ul>

CSS to style the first, last, even, and odd elements using CSS3 pseudo selectors

li:first-child { . . . }
li:last-child { . . . }
li:nth-of-type(even) { . . . }
li:nth-of-type(odd) { . . . }