diff --git src/wp-includes/class-wp-customize-manager.php src/wp-includes/class-wp-customize-manager.php
index 206d964..f96a4b7 100644
--- src/wp-includes/class-wp-customize-manager.php
+++ src/wp-includes/class-wp-customize-manager.php
@@ -3599,6 +3599,7 @@ final class WP_Customize_Manager {
 
 		$custom_css_setting = new WP_Customize_Custom_CSS_Setting( $this, sprintf( 'custom_css[%s]', get_stylesheet() ), array(
 			'capability' => 'unfiltered_css',
+			'default' => __( "/*\nYou can add your own CSS here.\n\nClick the help icon above to learn more.\n*/" ),
 		) );
 		$this->add_setting( $custom_css_setting );
 
@@ -3606,9 +3607,6 @@ final class WP_Customize_Manager {
 			'type'     => 'textarea',
 			'section'  => 'custom_css',
 			'settings' => array( 'default' => $custom_css_setting->id ),
-			'input_attrs' => array(
-				'placeholder' => __( "/*\nYou can add your own CSS here.\n\nClick the help icon above to learn more.\n*/" ),
-			)
 		) );
 	}
 
diff --git src/wp-includes/customize/class-wp-customize-custom-css-setting.php src/wp-includes/customize/class-wp-customize-custom-css-setting.php
index 2015458..17e01fc 100644
--- src/wp-includes/customize/class-wp-customize-custom-css-setting.php
+++ src/wp-includes/customize/class-wp-customize-custom-css-setting.php
@@ -128,7 +128,11 @@ final class WP_Customize_Custom_CSS_Setting extends WP_Customize_Setting {
 	 * @return string
 	 */
 	public function value() {
-		return wp_get_custom_css( $this->stylesheet );
+		$value = wp_get_custom_css( $this->stylesheet );
+		if ( empty( $value ) ) {
+			$value = $this->default;
+		}
+		return $value;
 	}
 
 	/**
diff --git tests/phpunit/tests/customize/custom-css-setting.php tests/phpunit/tests/customize/custom-css-setting.php
index d1d2a18..138f3a0 100644
--- tests/phpunit/tests/customize/custom-css-setting.php
+++ tests/phpunit/tests/customize/custom-css-setting.php
@@ -101,7 +101,7 @@ class Test_WP_Customize_Custom_CSS_Setting extends WP_UnitTestCase {
 	}
 
 	/**
-	 * Test WP_Customize_Custom_CSS_Setting::update().
+	 * Test crud methods on WP_Customize_Custom_CSS_Setting.
 	 *
 	 * @covers wp_get_custom_css()
 	 * @covers WP_Customize_Custom_CSS_Setting::value()
@@ -109,6 +109,10 @@ class Test_WP_Customize_Custom_CSS_Setting extends WP_UnitTestCase {
 	 * @covers WP_Customize_Custom_CSS_Setting::update()
 	 */
 	function test_crud() {
+
+		$this->setting->default = '/* Hello World */';
+		$this->assertEquals( $this->setting->default, $this->setting->value() );
+
 		$original_css = 'body { color: black; }';
 		$this->factory()->post->create( array(
 			'post_title' => $this->setting->stylesheet,