add_filter('next_posts_link_attributes', 'my_next_posts_link_attributes');
add_filter('previous_posts_link_attributes', 'my_previous_posts_link_attributes');
function my_next_posts_link_attributes() {
return 'class="archive-older"';
}
function my_previous_posts_link_attributes() {
return 'class="archive-newer"';
}