diff --git a/.gitignore b/.gitignore
index 89f03170..5886e439 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,7 +9,6 @@ wp-cli.yml
 
 # Allow local environment overrides.
 .wp-env.override.json
-.env/0-sandbox.php
 
 # Configs from wporg-repo-tools.
 .eslintrc.js
@@ -21,6 +20,9 @@ phpcs.xml.dist
 /source/wp-content/*
 /source/wp-content/themes/*
 
+# `.env/0-sandbox.php` is tracked, so these files can contain local tweaks that shouldn't be tracked.
+/source/wp-content/mu-plugins/sandbox-*.php
+
 # ...except the actual source of this project.
 !/source/wp-content/themes
 !/source/wp-content/themes/wporg-news-2021
diff --git a/.wp-env.json b/.wp-env.json
index 965418fe..af1176f6 100644
--- a/.wp-env.json
+++ b/.wp-env.json
@@ -6,7 +6,8 @@
 		"FS_METHOD": "direct",
 		"WP_ENVIRONMENT_TYPE": "local",
 		"JETPACK_DEV_DEBUG": true,
-		"WPORG_SANDBOXED": true
+		"WPORG_SANDBOXED": true,
+		"WPORG_GIT_MUPLUGINS_DIR": "/var/www/html/vendor/wporg/wporg-mu-plugins/mu-plugins"
 	},
 	"core": "WordPress/WordPress#5.8",
 	"plugins": [
@@ -20,6 +21,8 @@
 		"./source/wp-content/themes/wporg-news-2021"
 	],
 	"mappings": {
-		"env": "./env"
+		"env": "./env",
+		"wp-content/mu-plugins/0-sandbox.php": "./env/0-sandbox.php",
+		"vendor/wporg": "./vendor/wporg"
 	}
 }
diff --git a/composer.json b/composer.json
index 51126a4f..7e77b576 100644
--- a/composer.json
+++ b/composer.json
@@ -26,6 +26,10 @@
 		{
 			"type": "vcs",
 			"url": "git@github.com:WordPress/wporg-repo-tools.git"
+		},
+		{
+			"type": "vcs",
+			"url": "git@github.com:WordPress/wporg-mu-plugins.git"
 		}
 	],
 	"require": {},
@@ -37,6 +41,7 @@
 		"wpackagist-plugin/syntaxhighlighter": "*",
 		"wpackagist-plugin/wordpress-importer": "*",
 		"wporg/wporg-repo-tools": "dev-trunk",
+		"wordpress/wporg-mu-plugins": "dev-trunk",
 		"dealerdirect/phpcodesniffer-composer-installer": "^0.7.0",
 		"wp-coding-standards/wpcs": "2.*",
 		"phpcompatibility/phpcompatibility-wp": "*",
diff --git a/env/0-sandbox.php b/env/0-sandbox.php
new file mode 100644
index 00000000..617d453b
--- /dev/null
+++ b/env/0-sandbox.php
@@ -0,0 +1,11 @@
+<?php
+
+/*
+ * These are stubs for closed source code, or things that only apply to local environments.
+ */
+
+namespace WordPress_org\News_2021\Stubs;
+
+defined( 'WPINC' ) || die();
+
+require_once WPORG_GIT_MUPLUGINS_DIR . '/blocks/global-header-footer/blocks.php';
diff --git a/readme.md b/readme.md
index 8113543c..82fe3ced 100644
--- a/readme.md
+++ b/readme.md
@@ -21,9 +21,12 @@ This is starting as a fork of [Blockbase](https://github.com/Automattic/themes/t
 
 ### Environment management
 
+These must be run in the project's root folder, _not_ in theme/plugin subfolders.
+
 * Stop the environment: `yarn run env:stop` or `yarn run wp-env stop`
 * Restart the environment: `yarn run env` or `yarn run wp-env start`
 * Reset the dev site's content: `yarn run env:reset && yarn run env:import`
+* SSH into docker container: `docker exec -it {container ID} /bin/bash`. You can get the ID from `docker ps`.
 
 ### Asset management
 
diff --git a/source/wp-content/themes/wporg-news-2021/404.php b/source/wp-content/themes/wporg-news-2021/404.php
deleted file mode 100644
index 9101c74d..00000000
--- a/source/wp-content/themes/wporg-news-2021/404.php
+++ /dev/null
@@ -1,18 +0,0 @@
-<?php
-/**
- * The template for displaying 404 pages (not found)
- *
- * @package Blockbase
- * @since 1.1.1
- */
-get_header();
-?>
-	<main class="container-404">
-		<h1 class="has-text-align-center has-large-font-size"><?php _e( 'Oops! That page can&rsquo;t be found.', 'wporg' ); ?></h1>
-
-		<p><?php _e( 'It looks like nothing was found at this location. Maybe try a search?', 'wporg' ); ?></p>
-
-		<?php echo do_blocks('<!-- wp:search {"label":""} /-->'); ?>
-	</main>
-<?php
-get_footer();
diff --git a/source/wp-content/themes/wporg-news-2021/block-template-parts/footer.html b/source/wp-content/themes/wporg-news-2021/block-template-parts/footer.html
index 377c41c9..564215d6 100644
--- a/source/wp-content/themes/wporg-news-2021/block-template-parts/footer.html
+++ b/source/wp-content/themes/wporg-news-2021/block-template-parts/footer.html
@@ -1,7 +1 @@
-<!-- wp:group -->
-<div class="wp-block-group">
-	<!-- wp:paragraph {"align":"center","fontSize":"tiny"} -->
-	<p class="has-text-align-center has-tiny-font-size">Proudly Powered by <a href="https://wordpress.org" rel="nofollow">WordPress</a></p>
-	<!-- /wp:paragraph -->
-</div>
-<!-- /wp:group -->
+<!-- wp:wporg/global-footer /-->
diff --git a/source/wp-content/themes/wporg-news-2021/block-template-parts/header.html b/source/wp-content/themes/wporg-news-2021/block-template-parts/header.html
index 89a4df19..4ff56fe8 100644
--- a/source/wp-content/themes/wporg-news-2021/block-template-parts/header.html
+++ b/source/wp-content/themes/wporg-news-2021/block-template-parts/header.html
@@ -1,6 +1 @@
-<!-- wp:group {"align":"full","style":{"spacing":{"padding":{"bottom":"40px"}}},"className":"site-header"} -->
-<div class="wp-block-group alignfull site-header" style="padding-bottom:40px">
-	<!-- wp:site-title /-->
-	<!-- wp:navigation {"isResponsive":true,"__unstableLocation":"primary"} /-->
-</div>
-<!-- /wp:group -->
\ No newline at end of file
+<!-- wp:wporg/global-header /-->
diff --git a/source/wp-content/themes/wporg-news-2021/footer.php b/source/wp-content/themes/wporg-news-2021/footer.php
deleted file mode 100644
index 967b4b79..00000000
--- a/source/wp-content/themes/wporg-news-2021/footer.php
+++ /dev/null
@@ -1,11 +0,0 @@
-<footer class="wp-block-template-part site-footer-container">
-		<?php
-			echo gutenberg_block_template_part( 'footer' );
-		?>
-	</div>
-</footer>
-
-<?php wp_footer(); ?>
-
-</body>
-</html>
diff --git a/source/wp-content/themes/wporg-news-2021/functions.php b/source/wp-content/themes/wporg-news-2021/functions.php
index 661da7ac..8af03c45 100644
--- a/source/wp-content/themes/wporg-news-2021/functions.php
+++ b/source/wp-content/themes/wporg-news-2021/functions.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace WordPressdotorg\Theme\News;
+namespace WordPressdotorg\Theme\News_2021;
 
 /**
  * Actions and filters.
@@ -41,7 +41,6 @@ function theme_support() {
 			'primary' => __( 'Primary Navigation', 'wporg' ),
 		)
 	);
-
 }
 
 /**
@@ -69,7 +68,7 @@ function enqueue_assets() {
 /**
  * Add Google webfonts.
  *
- * @return $fonts_url
+ * @return string $fonts_url
  */
 function fonts_url() {
 	if ( ! class_exists( '\WP_Theme_JSON_Resolver_Gutenberg' ) ) {
diff --git a/source/wp-content/themes/wporg-news-2021/header.php b/source/wp-content/themes/wporg-news-2021/header.php
deleted file mode 100644
index 3f34c917..00000000
--- a/source/wp-content/themes/wporg-news-2021/header.php
+++ /dev/null
@@ -1,18 +0,0 @@
-<!DOCTYPE html>
-<html <?php language_attributes(); ?>>
-<head>
-	<meta charset="<?php bloginfo( 'charset' ); ?>" />
-	<meta name="viewport" content="width=device-width, initial-scale=1" />
-	<link rel="profile" href="https://gmpg.org/xfn/11" />
-	<?php wp_head(); ?>
-</head>
-
-<body <?php body_class(); ?>>
-<?php wp_body_open(); ?>
-
-	<div class="wp-site-blocks">
-		<header class="wp-block-template-part">
-			<?php
-				echo gutenberg_block_template_part( 'header' );
-			?>
-		</header>
diff --git a/source/wp-content/themes/wporg-news-2021/index.php b/source/wp-content/themes/wporg-news-2021/index.php
deleted file mode 100644
index 62200328..00000000
--- a/source/wp-content/themes/wporg-news-2021/index.php
+++ /dev/null
@@ -1,2 +0,0 @@
-<?php
-// Silence is golden.