Problem with query param in main URL of website

Hi there,

In advance, thanks for the effort building and maintaining the plugin.

If the main URL of a website has been configured in a way that it contains a query parameter, for example https://test.com/?attr=123, then the plugin doesn’t load the custom CSS correctly, in this example it creates the URL https://test.com/?attr=123%3Fdisplay_custom_css%3Dcss

A suggestion is to change the line where the CSS is registered by:

wp_register_style( 'wp-add-custom-css', get_home_url(null, '?display_custom_css=css') );