How to customize 'read more'

Question

I'm trying to add a button to every post excerpt. But I get the button without href:

function new_excerpt_more( $more ) {                    
    global $post;
    return "<p><a href='" .get_permalink( $post->ID ) ."' class='btn' >Read more</a></p>";
}
add_filter('excerpt_more', 'new_excerpt_more');

The problem only occurs when I'm showing the excerpts with a shortcode command within the content:

function show_last_articles() {
    $args = array( 'posts_per_page' => 3, 'category_name' => 'xyz');
    $lastposts = get_posts( $args );
    foreach ( $lastposts as $post ):
        setup_postdata( $post );
            $return = "<div class='excerpts'>";
            $return .= "<h2><a href='" .get_the_permalink( $post->ID ) ."'>" .get_the_title( $post->ID ) ."</a></h2>";
            $return .= "<div>" .get_the_excerpt( $post->ID ) ."</div>";
            $return .= "</div>";
    endforeach; 
    wp_reset_postdata();
    return $return;
}
add_shortcode( 'last_articles', 'show_last_articles');

Whats wrong?

Answer 1

This only makes the read more link a button.

add_filter( 'excerpt_more', 'wpsites_read_more_link' );
    function wpsites_read_more_link( $more ) {
        return '... <a class="more-link button" href="' . get_permalink() . '">Continue Reading</a>';
}

Replace the button class with your themes button class.