将下列代码放到主题目录下的functions.php文件里即可。

add_action( 'customize_register', 'prefix_remove_css_section', 15 );

function prefix_remove_css_section( $wp_customize ) {
  $wp_customize->remove_section( 'title_tagline');
  $wp_customize->remove_section( 'colors');
  $wp_customize->remove_section( 'header_image');
  $wp_customize->remove_section( 'background_image');
  $wp_customize->remove_panel( 'nav_menus');
  $wp_customize->remove_section( 'static_front_page');
  $wp_customize->remove_section( 'custom_css'); 
}