当然，您可以使用customize_controls_enqueue_scripts 钩子加载自定义CSS和JS。

这是制作400px面板的一个示例：

文件：sample-theme/css/customizer-controls.css

.wp-full-overlay.expanded {
    margin-left: 400px;
}
.wp-full-overlay-sidebar {
    min-width: 400px;
}
.wp-full-overlay.collapsed .wp-full-overlay-sidebar {
    margin-left: -400px;
}

/**
 * Enqueue style for customized customizer.
 */
 function sample_theme_customize_enqueue() {
     wp_enqueue_style( \'custom-customize\', get_theme_file_uri( \'css/sample-theme-customizer-controls.css\' ) );
 }

 add_action( \'customize_controls_enqueue_scripts\', \'sample_theme_customize_enqueue\' );