functions.php

<?php //don't include this line

/**
 * Class on excerpt more 
 *
 */
function be_dps_excerpt_more_class( $output, $original_atts, $image, $title, $date, $excerpt, $inner_wrapper, $content, $class, $author, $category_display_text ) {
 if( !empty( $excerpt ) )
    $output = str_replace( $excerpt, '<span class="excerpt-more">' . $excerpt . '</span>', $output );
 return $output;
}
add_filter( 'display_posts_shortcode_output', 'be_dps_excerpt_more_class', 10, 11 );