WordPress styling of admin according to current page/post/etc template

block-editor-admin.css

/* CSS for different templates, some examples below */

.post-type-page.sky-full-width .editor-styles-wrapper {
  padding-bottom: var(--wp--preset--spacing--80);
  background-color: var(--wp--preset--color--sky);
  background-image: url("../images/[email protected]");
  background-size: 300px 300px;
}

.post-type-page:not(.default-page-template) .editor-styles-wrapper .nt-page__content-wrap {
  position: static;
  top: auto;
  margin-top: var(--wp--preset--spacing--80);
}

.post-type-page.default-page-template .editor-styles-wrapper {
  background-color: var(--wp--preset--color--sky);
  background-image: url("../images/[email protected]");
  background-size: 300px 300px;
  padding-bottom: var(--wp--preset--spacing--80);
}

.post-type-page.default-page-template .editor-styles-wrapper .block-editor-block-list__layout.is-root-container {
  padding-bottom: var(--wp--preset--spacing--80);
}

.post-type-page.default-page-template .editor-styles-wrapper .block-editor-block-list__layout.is-root-container > .alignfull,
.post-type-page.default-page-template .editor-styles-wrapper .block-editor-block-list__layout.is-root-container > .alignwide {
  max-width: 736px;
  width: 100%;
  margin-left: auto;
  margin-right: auto;
}

.post-type-page .editor-post-title.wp-block-post-title,
.post-type-page .is-style-h1,
.post-type-page .wp-block-heading.is-style-h1,
.post-type-page .editor-styles-wrapper h1 {
  font-size: var(--wp--custom--font-size--page-title);
  font-family: var(--wp--custom--font-family--body);
  letter-spacing: var(--wp--custom--letter-spacing--page-title);
  line-height: var(--wp--custom--line-height--page-title);
  font-weight: 700;
}

.post-type-page .editor-styles-wrapper h3,
.post-type-page .is-style-h3,
.post-type-page h2.wp-block-heading.is-style-h3,
.post-type-page .wp-block-heading.is-style-h3 {
  font-weight: 700;
  font-size: var(--wp--custom--heading-size--4);
  letter-spacing: var(--wp--custom--letter-spacing--h-4);
}

.post-type-page .editor-styles-wrapper h3 a,
.post-type-page .is-style-h3 a,
.post-type-page h2.wp-block-heading.is-style-h3 a,
.post-type-page .wp-block-heading.is-style-h3 a {
  border-bottom: none;
}

functions.php

<?php
/**
 * Admin body classes
 * 
 * @link https://developer.wordpress.org/reference/hooks/admin_body_class/
 * @link https://kellenmace.com/get-page-template-post-wordpress-admin/
*/

function clientname_admin_body_classes( $classes ) {

	$classes .= ' client-name-admin';

	$clientname_current_template = get_post_meta( get_the_ID(), '_wp_page_template', true ); 
	$clientname_post_type = get_post_type();

	// posts
	if ( $clientname_post_type === 'post' ){

		if ( empty( $clientname_current_template ) || $clientname_current_template === 'default' || $clientname_current_template == 'single-no-ads.php' ) {

			$classes .= ' single-standard';	

		} elseif ( $clientname_current_template === 'single-alternate.php' || $clientname_current_template === 'single-alternate-no-ads.php' ) {

			$classes .= ' single-alternate';
		}

	// pages
	} elseif ( $clientname_post_type === 'page' ) {

		if ( empty( $clientname_current_template ) || $clientname_current_template === 'default' ) {

			$classes .= ' default-page-template';
			
		} elseif ( $clientname_current_template === 'template-no-title-sky.php' ) {

			$classes .= ' full-width-template sky-full-width';		

		} elseif ( $clientname_current_template === 'template-home.php' || $clientname_current_template === 'template-no-title.php' || $clientname_current_template === 'template-no-title-no-header-footer.php' ) {

			$classes .= ' full-width-template nt-noise-bg';
			
		}
	}

	return $classes;
}

add_filter( 'admin_body_class', 'clientname_admin_body_classes' );


/**
*
* Admin stylesheet for styling different page/post templates
*
*/

function clientname_block_styles() {

    wp_enqueue_style( 
        'client-name-editor-admin', 
        get_stylesheet_directory_uri() . '/assets/css/block-editor-admin.css',
        array(),
        // false,
        filemtime( get_stylesheet_directory() . '/assets/css/block-editor-admin.css' )
    );
}
add_action( 'enqueue_block_editor_assets', 'clientname_block_styles' );