Ticket #38493: 38493.1.diff

src/wp-includes/class-wp-customize-control.php

@@ -532 +532 @@
                                         if ( ! empty( $this->description ) ) : ?>
                                                 <span class="description customize-control-description"><?php echo $this->description; ?></span>
                                         <?php endif; ?>
-                                        <textarea rows="5" <?php $this->link(); ?>><?php echo esc_textarea( $this->value() ); ?></textarea>
+                                        <textarea rows="5" <?php $this->input_attrs(); ?> <?php $this->link(); ?>><?php echo esc_textarea( $this->value() ); ?></textarea>
                                 </label>
                                 <?php
                                 break;

src/wp-includes/class-wp-customize-manager.php

@@ -3393 +3393 @@
                         '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*/" ),
+                        )
                 ) );
         }