Hi There,
Thank you for the clarification, now I understand what is the issue here and regretfully it can’t be resolve with just CSS.
Basically your custom CSS above should also applied on the audio post, because technically all posts (including the audio) are also single posts (that is the .single on your selector). Unfortunately it was not the case, because unlike standard post the audio post’s entry-header is a sibling of entry-featured. Unlike on the standard post the entry-header is a child of entry-featured.
So what we need to do now is to modify the content-audio.php file to make the entry-header a child of entry-featured. Good thing you have already a child theme.
On your child theme navigate to this directory: /x-child/framework/views/icon/ and create a file named content-audio.php and paste the code below on it:
<?php
// =============================================================================
// VIEWS/ICON/CONTENT-AUDIO.PHP
// -----------------------------------------------------------------------------
// Audio post output for Icon.
// =============================================================================
?>
<article id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
<div class="entry-wrap">
<?php x_icon_comment_number(); ?>
<div class="x-container max width">
<div class="entry-featured">
<?php x_get_view( 'icon', '_content', 'post-header' ); ?>
<?php if ( has_post_thumbnail() ) : ?>
<div class="entry-thumb">
<?php echo get_the_post_thumbnail( get_the_ID(), 'entry', NULL ); ?>
</div>
<?php x_featured_audio(); ?>
</div>
<?php else : ?>
<div class="entry-featured">
<?php x_featured_audio(); ?>
</div>
<?php endif; ?>
<?php if ( is_single() ) : ?>
<?php x_get_view( 'global', '_content', 'the-content' ); ?>
<?php endif; ?>
</div>
</div>
</article>
And that should apply your custom CSS above to the audio post without editing or adding a line. Keep in mind that this is already fall on custom development, regretfully we can not provide further customization support from here. Thank you for understanding.
Another thing, I see that your X and Cornerstone is a few update behind, we’ve just release a maintenance update addressing a handful of issues. (see the Changelog for details.)
Please update to X 5.2.2 / Cornerstone 2.1.2
Remember to clear all caches after updating so that the code from the latest release is always in use. This will help you to avoid any potential errors.
Hope it helps,
Cheers!