Adding plugin folder for the project.

plugin/index.php

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+<?php
+
+/**
+ * Plugin Name: Gutenberg
+ * Plugin URI: https://wordpress.github.io/gutenberg/
+ * Description: Prototyping since 1440. Development plugin for the editor focus in core.
+ * Version: 0.1
+ */
+
+add_action( 'admin_menu', 'gutenberg_menu' );
+
+function gutenberg_menu() {
+	add_menu_page(
+		'Gutenberg',
+		'Gutenberg',
+		'manage_options',
+		'gutenberg',
+		'the_gutenberg_project'
+	);
+}
+
+function gutenberg_scripts_and_styles( $hook ) {
+	if ( $hook === 'toplevel_page_gutenberg' ) {
+		wp_enqueue_style( 'gutenberg_css', plugins_url( 'style.css', __FILE__ ) );
+	}
+}
+add_action( 'admin_enqueue_scripts', 'gutenberg_scripts_and_styles' );
+
+function the_gutenberg_project() {
+	?>
+	<div class="gutenberg">
+		<section class="gutenberg__editor" contenteditable="true">
+			<h2>1.0 Is The Loneliest Number</h2>
+			<p>Many entrepreneurs idolize Steve Jobs. He’s such a <a href=""><span class="space-sep">&nbsp;</span>perfectionist<span class="space-sep-end">&nbsp;</span></a>, they say. Nothing leaves the doors of 1 Infinite Loop in Cupertino without a polish and finish that makes geeks everywhere drool. No compromise!</p>
+			<img alt="" src="https://cldup.com/HN3-c7ER9p.jpg" />
+			<p>I like Apple for the opposite reason: they’re not afraid of getting a rudimentary 1.0 out into the world.</p>
+		</section>
+	</div>
+	<?php
+}

plugin/style.css

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+.gutenberg {
+	background: #fff;
+	margin: -20px 0 0 -20px;
+	padding: 60px;
+}
+
+.gutenberg__editor {
+	max-width: 700px;
+	margin: 0 auto;
+}
+
+.gutenberg__editor img {
+	max-width: 100%;
+}