Solution:
Look into wordpress/wp-includes/class-wp-admin-bar.php at the beginning, and you will find this. Watch closely the comments for the actual answer:
if ( current_theme_supports( ‘admin-bar’ ) ) {
/**
* To remove the default padding styles
* from WordPress for the Toolbar,
* use the following code:
* add_theme_support( ‘admin-bar’, array( ‘callback’ => ‘__return_false’ ) );
*/
$admin_bar_args = get_theme_support( ‘admin-bar’ );
$header_callback = $admin_bar_args[0][‘callback’];
}
if ( empty($header_callback) )
$header_callback = ‘_admin_bar_bump_cb’;
add_action(‘wp_head’, $header_callback);
wordpress/wp-includes/admin-bar.php contains the default implementation of _admin_bar_bump_cb:
/**
* Default admin bar callback.
*
* @since 3.1.0
*/
function _admin_bar_bump_cb() { ?>
<style type=”text/css” media=”screen”>
html { margin-top: 28px !important; }
* html body { margin-top: 28px !important; }
</style>
<?php
}