Function Reference/sticky class
This function has been deprecated since Version 3.5. That means it has been replaced by a new function or is no longer supported, and may be removed from future versions. All code that uses this function should be converted to use its replacement if one exists. See also
Displays the Sticky Posts class on a post if applicable. This tag must be within The Loop.
<?php sticky_class(); ?>
This tag has no parameters.
<div class="post<?php sticky_class(); ?>" id="post-<?php the_ID(); ?>">
Sticky Post Identifier
Provides a sticky class to each post that it applies to: