Popup / hidden color section is only hidden after popup opens.

Hello.

I need a pop-up after clicking on “buchen”.
The content (a booking field) should be only shown in the popup, but it is still visible on the bottom of the Side.
Which css can I give the Popup-content, so he only shows up in the popup?

What I did:

1.:
I Added the following PHP Code:

function add_custom_script(){
?>
<script>
jQuery(window).load(function(){

jQuery(‘.open-popup-link’).magnificPopup({
type:’inline’,
midClick: true
});

});
</script>
<?php
}
add_action(‘wp_footer’, ‘add_custom_script’);

2.:
I build a color Section and gave it the ID: content-to-open.

3.:
I gave the button this code:
Buchen