Introduce file for sharing CSS for content between editor and renderer

[MAILPOET-6249]

packages/php/email-editor/src/Engine/Renderer/ContentRenderer/ContentRenderer.php

@@ -89,6 +89,7 @@ class ContentRenderer {
    */
   private function inlineStyles($html, WP_Post $post, $template = null) {
     $styles = (string)file_get_contents(dirname(__FILE__) . '/' . self::CONTENT_STYLES_FILE);
+    $styles .= (string)file_get_contents(dirname(__FILE__) . '/../../content-shared.css');
 
     // Apply default contentWidth to constrained blocks.
     $layout = $this->themeController->getLayoutSettings();

packages/php/email-editor/src/Engine/SettingsController.php

@@ -56,8 +56,10 @@ class SettingsController {
     // Assets for iframe editor (component styles, scripts, etc.)
     $settings['__unstableResolvedAssets'] = $this->iframeAssets;
     $editorContentStyles = file_get_contents(__DIR__ . '/content-editor.css');
+    $sharesContentStyles = file_get_contents(__DIR__ . '/content-shared.css');
     $settings['styles'] = [
       ['css' => $editorContentStyles],
+      ['css' => $sharesContentStyles],
     ];
 
     $settings['__experimentalFeatures'] = $themeSettings;

packages/php/email-editor/src/Engine/content-shared.css

@@ -0,0 +1,15 @@
+/*
+ * Styles for both the email editor and renderer.
+ */
+
+/* Automatic padding for blocks with background color */
+.email-text-block.has-background,
+p.has-background,
+h1.has-background,
+h2.has-background,
+h3.has-background,
+h4.has-background,
+h5.has-background,
+h6.has-background {
+  padding: 16px 24px;
+}