diff --git a/src/wp-content/themes/twentytwelve/css/editor-blocks.css b/src/wp-content/themes/twentytwelve/css/editor-blocks.css
index d9efec32d59b7..29eb1f7ede596 100644
--- a/src/wp-content/themes/twentytwelve/css/editor-blocks.css
+++ b/src/wp-content/themes/twentytwelve/css/editor-blocks.css
@@ -369,6 +369,7 @@ p.has-drop-cap:not(:focus)::first-letter {
 	background-image: -o-linear-gradient(top, #f4f4f4, #e6e6e6);
 	background-image: linear-gradient(to bottom, #f4f4f4, #e6e6e6);
 	background-repeat: repeat-x;
+	color: #7c7c7c;
 }
 
 /* Separator */
diff --git a/src/wp-content/themes/twentytwenty/assets/css/editor-style-block-rtl.css b/src/wp-content/themes/twentytwenty/assets/css/editor-style-block-rtl.css
index 063075bf1ab31..2c3192b00fcd1 100644
--- a/src/wp-content/themes/twentytwenty/assets/css/editor-style-block-rtl.css
+++ b/src/wp-content/themes/twentytwenty/assets/css/editor-style-block-rtl.css
@@ -920,8 +920,8 @@ hr.wp-block-separator.is-style-dots::before {
 
 /* Block: Button ----------------------------- */
 
-.editor-styles-wrapper .wp-block-button__link,
-.editor-styles-wrapper .wp-block-file__button {
+:root .editor-styles-wrapper .wp-block-button__link,
+:root .editor-styles-wrapper .wp-block-file__button {
 	background: #cd2653;
 	border-radius: 0;
 	color: #fff;
@@ -937,6 +937,11 @@ hr.wp-block-separator.is-style-dots::before {
 	line-height: 1.1;
 }
 
+.editor-styles-wrapper .wp-block-button__link:hover,
+.editor-styles-wrapper .wp-block-file__button:hover {
+	text-decoration: underline;
+}
+
 /* BUTTON STYLE: OUTLINE */
 
 .editor-styles-wrapper .is-style-outline .wp-block-button__link,
@@ -1301,8 +1306,8 @@ hr.wp-block-separator.is-style-dots::before {
 
 	/* BLOCK: BUTTON */
 
-	.editor-styles-wrapper .wp-block-button__link,
-	.editor-styles-wrapper .wp-block-file__button {
+	:root .editor-styles-wrapper .wp-block-button__link,
+	:root .editor-styles-wrapper .wp-block-file__button {
 		font-size: 17px;
 	}
 
diff --git a/src/wp-content/themes/twentytwenty/assets/css/editor-style-block.css b/src/wp-content/themes/twentytwenty/assets/css/editor-style-block.css
index 8b62985520683..18e83281076db 100644
--- a/src/wp-content/themes/twentytwenty/assets/css/editor-style-block.css
+++ b/src/wp-content/themes/twentytwenty/assets/css/editor-style-block.css
@@ -924,8 +924,8 @@ hr.wp-block-separator.is-style-dots::before {
 
 /* Block: Button ----------------------------- */
 
-.editor-styles-wrapper .wp-block-button__link,
-.editor-styles-wrapper .wp-block-file__button {
+:root .editor-styles-wrapper .wp-block-button__link,
+:root .editor-styles-wrapper .wp-block-file__button {
 	background: #cd2653;
 	border-radius: 0;
 	color: #fff;
@@ -941,6 +941,11 @@ hr.wp-block-separator.is-style-dots::before {
 	line-height: 1.1;
 }
 
+.editor-styles-wrapper .wp-block-button__link:hover,
+.editor-styles-wrapper .wp-block-file__button:hover {
+	text-decoration: underline;
+}
+
 /* BUTTON STYLE: OUTLINE */
 
 .editor-styles-wrapper .is-style-outline .wp-block-button__link,
@@ -1305,8 +1310,8 @@ hr.wp-block-separator.is-style-dots::before {
 
 	/* BLOCK: BUTTON */
 
-	.editor-styles-wrapper .wp-block-button__link,
-	.editor-styles-wrapper .wp-block-file__button {
+	:root .editor-styles-wrapper .wp-block-button__link,
+	:root .editor-styles-wrapper .wp-block-file__button {
 		font-size: 17px;
 	}
 
diff --git a/src/wp-includes/css/classic-themes.css b/src/wp-includes/css/classic-themes.css
new file mode 100644
index 0000000000000..d77a25a3b95a4
--- /dev/null
+++ b/src/wp-includes/css/classic-themes.css
@@ -0,0 +1,18 @@
+/**
+ * These rules are needed for backwards compatibility.
+ * They should match the button element rules in the base theme.json file.
+ */
+.wp-block-button__link {
+	color: #ffffff;
+	background-color: #32373c;
+	border-radius: 9999px; /* 100% causes an oval, but any explicit but really high value retains the pill shape. */
+
+	/* This needs a low specificity so it won't override the rules from the button element if defined in theme.json. */
+	box-shadow: none;
+	text-decoration: none;
+
+	/* The extra 2px are added to size solids the same as the outline versions.*/
+	padding: calc(0.667em + 2px) calc(1.333em + 2px);
+
+	font-size: 1.125em;
+}
diff --git a/src/wp-includes/default-filters.php b/src/wp-includes/default-filters.php
index 1d69c809e0ce6..e9ca31f5f7908 100644
--- a/src/wp-includes/default-filters.php
+++ b/src/wp-includes/default-filters.php
@@ -560,7 +560,6 @@
 add_action( 'wp_enqueue_scripts', 'wp_enqueue_classic_theme_styles' );
 add_action( 'admin_enqueue_scripts', 'wp_localize_jquery_ui_datepicker', 1000 );
 add_action( 'admin_enqueue_scripts', 'wp_common_block_scripts_and_styles' );
-add_action( 'admin_enqueue_scripts', 'wp_enqueue_classic_theme_styles' );
 add_action( 'enqueue_block_assets', 'wp_enqueue_registered_block_scripts_and_styles' );
 add_action( 'enqueue_block_assets', 'enqueue_block_styles_assets', 30 );
 add_action( 'enqueue_block_editor_assets', 'wp_enqueue_registered_block_scripts_and_styles' );
@@ -572,6 +571,7 @@
 add_filter( 'print_scripts_array', 'wp_prototype_before_jquery' );
 add_filter( 'customize_controls_print_styles', 'wp_resource_hints', 1 );
 add_action( 'admin_head', 'wp_check_widget_editor_deps' );
+add_filter( 'block_editor_settings_all', 'wp_add_editor_classic_theme_styles' );
 
 // Global styles can be enqueued in both the header and the footer. See https://core.trac.wordpress.org/ticket/53494.
 add_action( 'wp_enqueue_scripts', 'wp_enqueue_global_styles' );
diff --git a/src/wp-includes/script-loader.php b/src/wp-includes/script-loader.php
index 6f844cbc7e984..fd1bf4b6fa93b 100644
--- a/src/wp-includes/script-loader.php
+++ b/src/wp-includes/script-loader.php
@@ -3658,16 +3658,48 @@ function _wp_theme_json_webfonts_handler() {
 }
 
 /**
- * Loads classic theme styles on classic themes.
+ * Loads classic theme styles on classic themes in the frontend.
  *
  * This is needed for backwards compatibility for button blocks specifically.
  *
  * @since 6.1.0
  */
 function wp_enqueue_classic_theme_styles() {
-	if ( ! wp_is_block_theme() ) {
+	if ( ! WP_Theme_JSON_Resolver::theme_has_support() ) {
 		$suffix = wp_scripts_get_suffix();
-		wp_register_style( 'classic-theme-styles', "/wp-includes/css/dist/block-library/classic$suffix.css", array(), true );
+		wp_register_style( 'classic-theme-styles', '/' . WPINC . "/css/classic-themes$suffix.css", array(), true );
 		wp_enqueue_style( 'classic-theme-styles' );
 	}
 }
+
+/**
+ * Loads classic theme styles on classic themes in the editor.
+ *
+ * This is needed for backwards compatibility for button blocks specifically.
+ *
+ * @since 6.1.0
+ *
+ * @param array $editor_settings The array of editor settings.
+ * @return array A filtered array of editor settings.
+ */
+function wp_add_editor_classic_theme_styles( $editor_settings ) {
+	if ( WP_Theme_JSON_Resolver::theme_has_support() ) {
+		return $editor_settings;
+	}
+	$suffix = wp_scripts_get_suffix();
+	$classic_theme_styles = ABSPATH . WPINC . "/css/classic-themes$suffix.css";
+
+	// This follows the pattern of get_block_editor_theme_styles,
+	// but we can't use get_block_editor_theme_styles directly as it
+	// only handles external files or theme files.
+	$classic_theme_styles_settings = array(
+		'css'            => file_get_contents( $classic_theme_styles ),
+		'__unstableType' => 'core',
+		'isGlobalStyles' => false,
+	);
+
+	// Add these settings to the start of the array so that themes can override them.
+	array_unshift( $editor_settings['styles'], $classic_theme_styles_settings );
+
+	return $editor_settings;
+}