WP - 显示特定页面的缩略图

Question

Trying to include a specific page on the frontpage of a WordPress Theme.

The overal HTML structure should be similar to this:

<div>
     <h1>Om</h1>
     <p>Content comes here</p>
</div>

<div style="background-image: url(...)">
</div>

At the moment it echos the content of the page successfully.

Here is how that part works with PHP:

<div class="omtekst col-md-6 half-content-wrapper">
    <h1 class="semibold">Om</h1>
    <?php
        $my_id = 7;
        $post_id_7 = get_post($my_id);
        $content = $post_id_7->post_content;
        $content = apply_filters('the_content', $content);
        $content = str_replace(']]>', ']]>', $content);
        echo $content;
    ?>
</div>

As mentioned earlier I want to include the thumbnail below this. This is where I am having problems.

However, I have started on the PHP to show how I am thinking. The thumbnail should be $image or similar.

<div class="ombilde col-md-6" style="background-image: url('<?php echo $image; ?>')">

Do you have a working solution for this?

Edit

My custom thumb which is not used with this image:

add_action( 'after_setup_theme', 'mytheme_custom_thumbnail_size' );
function mytheme_custom_thumbnail_size(){
    add_image_size( 'frontpage_thumb', 500 ); // Unlimited height
}

Enabled post thumbnails:

if ( function_exists( 'add_theme_support' ) ) { 
    add_theme_support( 'post-thumbnails' ); 
    add_theme_support( 'nav-menus' );
    add_theme_support( 'widgets' );
}

Answer 1

to get the url of image you can use

$image = wp_get_attachment_image_src( get_post_thumbnail_id([ID_HERE]), [IMAGE SIZE HERE] );

then you can use

<div class="ombilde col-md-6" style="background-image: url('<?php echo $image[0]; ?>')">

to get image size string look at your theme for "add_image_size" function

and as pgk said post-thumbnails have to be enabled inside functions but i guess you already did this

edit:

[ID_HERE] replace with post id

[IMAGE SIZE HERE] you can test this with "full"