The Problem

We need to add our custom class(es) to the posts navigation links to be able to add some styles.

The Solution

Use the available next_posts_link_attributes and previous_posts_link_attributes hooks.

How?

Open your theme’s function.php file and add these lines (must be inside the <?php ?> tag):

add_filter( 'next_posts_link_attributes', 'kc_next_post_link_attr' );
add_filter( 'previous_posts_link_attributes', 'kc_prev_post_link_attr' );

function kc_next_post_link_attr() {
	return 'class="next-page"';
}

function kc_prev_post_link_attr() {
	return 'class="prev-page"';
}