*** a/wp-content/themes/twentytwelve/editor-style.css
--- b/wp-content/themes/twentytwelve/editor-style.css
@@
 /* Block Editor compatibility */
 
+/* Fix heading typography for post title field */
+.editor-post-title__input {
+	font-size: 28px;
+	font-weight: normal;
+	line-height: 1.3;
+	margin: 0 0 20px;
+}
+
 /* Paragraph block */
 .block-editor-block-list__block.wp-block-paragraph {
 	margin-bottom: 24px;