要覆盖Gutenberg的样式，您需要添加自己的样式表。因此，钩住enqueue_block_editor_assets 然后添加您自己的样式表，在其中以要覆盖的选择器为目标。在下面的示例中，我在自定义主题的assets/ 文件夹

functions.php:

// Add backend styles for Gutenberg.
add_action(\'enqueue_block_editor_assets\', \'gutenberg_editor_assets\');

function gutenberg_editor_assets() {
  // Load the theme styles within Gutenberg.
  wp_enqueue_style(\'my-gutenberg-editor-styles\', get_theme_file_uri(\'/assets/gutenberg-editor-styles.css\'), FALSE);
}

assets/gutenberg-editor-styles.css:

.editor-post-title__input {
  border: 1px solid black;
}