This will likely be done in your theme’s index.php …
Find..
<?php if (have_posts()) : while (have_posts()) : ?>
or
<?php while (have_posts()) : ?>
Update that to…
<?php if (have_posts()) : $postCount = 1; while (have_posts()) : $postCount++; ?>
Then find where you post element starts…
Here’s an example:
<div class="post" id="post-<?php the_ID(); ?>">
Now update that to..
<div <?php if($postCount == 1) { ?>class="specialclass"<?php } else { ?>class="post"<?php } ?> id="post-<?php the_ID(); ?>">
All posts except the first will have the usual post class, the first will have “specialclass”, but you can change the name to whatever you want…
Hope that helps.. ??
NOTE: If on the first part you only had.
<?php while (have_posts()) : ?>
You’ll then also need to update this area…
<?php endwhile; ?>
to
<?php endwhile; endif; ?>