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<?php

// Class for each links

function ccd_posts_link_attributes_2() {
    return 'class="next-post"';
}

function ccd_posts_link_attributes_1() {
    return 'class="prev-post"';
}

add_filter( 'next_posts_link_attributes', 'ccd_posts_link_attributes_1' );
add_filter( 'previous_posts_link_attributes', 'ccd_posts_link_attributes_2' );

?>

<?php

// Single class for both links

function ccd_posts_link_attributes() {
    return 'class="next-prev-post"';
}

add_filter( 'next_posts_link_attributes', 'ccd_posts_link_attributes' );
add_filter( 'previous_posts_link_attributes', 'ccd_posts_link_attributes' );

?>