example chromeless style override

Style a specific admin page inside the iframe

Chromeless iframes load the admin page with most WordPress chrome hidden, but the page's own CSS still applies. Use openstation_chromeless_styles to append overrides inside the iframe only.

<?php
/**
 * Plugin Name: Tighten Posts List Inside Desktop
 */
defined( 'ABSPATH' ) || exit;

add_action( 'openstation_chromeless_styles', function () {
    // Only applies to the iframe's chromeless request, not the parent shell.
    wp_add_inline_style(
        'os-chromeless',
        '
        body.edit-php .wp-list-table { border-radius: 6px; overflow: hidden; }
        body.edit-php .subsubsub { margin-block: 4px 8px; }
        body.upload-php #wpbody-content { padding-top: 4px; }
        '
    );
} );

Why scope via a body class

The chromeless CSS is loaded into every iframe. WordPress adds page-specific body classes (body.edit-php, body.upload-php, etc.), which lets you scope overrides to just the page you want without polluting others.

When to use this vs. the shell-side CSS

• This hook (openstation_chromeless_styles) — tweaks inside the iframe: a form, a list table, a sidebar, an editor canvas.
• Your own admin_enqueue_scripts handler — parent shell changes: dock styling, window chrome, wallpaper.

If in doubt: the iframe contains WordPress admin pages; the shell contains windows that contain iframes.

Related

• Hooks Reference — openstation_chromeless_styles
• Hooks Reference — openstation_chromeless_after