Depending on your use-case, you may want to change the width of your customizer, thus having more real-estate to handle your custom controls and content. You can do that by adding some custom CSS.

Using the WordPress API:

First, add a new CSS file in your plugin/theme with the following in it:

.wp-full-overlay-sidebar {
    width: 400px;
}

.wp-full-overlay.expanded {
    margin-left: 400px;
}

If this is a theme we’re talking about, then I’ll assume this file is located in {THEME}/assets/css/customizer.css.

Then, add the following to your functions.php file:

<?php

function add_my_customizer_styles() {
    wp_enqueue_style( 'my-customizer-css', trailingslashit( get_template_directory_uri() ).'assets/css/customizer.css', null );
}
add_action( 'customize_controls_print_styles', 'add_my_customizer_styles', 99 );

?>

Using Kirki

Alternatively, if you’re using the Kirki Toolkit plugin you can do it by using the width argument in your configuration. For more info please check out the plugin’s Wiki page.