Add CSS to CPT

### Code Example:

function custom_enqueue_css_for_single_cpt() {
    // Check if we're on a single page and of the specific custom post type.
    if (is_singular('your_custom_post_type')) {
        wp_enqueue_style(
            'custom-cpt-style', // Handle for the stylesheet.
            get_stylesheet_directory_uri() . '/css/custom-cpt-style.css', // Path to your CSS file.
            array(), // Dependencies.
            '1.0.0', // Version number.
            'all' // Media type.
        );
    }
}
add_action('wp_enqueue_scripts', 'custom_enqueue_css_for_single_cpt');

### Steps:
1. Replace `your_custom_post_type` with the slug of your custom post type.
2. Replace `/css/custom-cpt-style.css` with the path to your CSS file relative to your theme directory.
3. Save the code in your theme's `functions.php` file or in a custom plugin.

### Explanation:
– **`is_singular('your_custom_post_type')`**: Checks if the current page is a single page of the specified custom post type.
– **`wp_enqueue_style`**: Adds your CSS file to the page.

### Alternative: Inline CSS
If you prefer to include inline CSS instead of a separate file:

function custom_inline_css_for_single_cpt() {
    if (is_singular('your_custom_post_type')) {
        echo '<style>
            .your-css-class {
                color: #333;
                font-size: 18px;
            }
        </style>';
    }
}
add_action('wp_head', 'custom_inline_css_for_single_cpt');

This approach is useful for small style changes without needing a separate file.

### Example 1: Using `get_the_ID()`
The `get_the_ID()` function works inside **The Loop** or on single post pages.

$post_id = get_the_ID();
echo $post_id;

### Example 2: Using the `$post` Global Variable
If you're outside The Loop, you can use the `$post` global variable:

global $post;
$post_id = $post->ID;
echo $post_id;

### Example 3: Using `get_queried_object_id()`
For more generic cases, like outside single post templates or The Loop, you can use `get_queried_object_id()`:

$post_id = get_queried_object_id();
echo $post_id;

### When to Use Each Method:
– **`get_the_ID()`**: Use this inside The Loop or single post pages.
– **`$post->ID`**: Use this when accessing the global `$post` variable outside The Loop.
– **`get_queried_object_id()`**: Use this for retrieving the ID of the queried object, such as on a post, page, or archive template.

### Example in Context:
If you want to add the current post ID to the body class, for instance:

add_filter('body_class', function ($classes) {
    if (is_singular()) {
        $classes[] = 'post-id-' . get_the_ID();
    }
    return $classes;
});

This will append the current post ID as a CSS class to the “ tag.