Additional CSS not saving

I’m trying to add the following to “additional CSS” in the customizer:

@media only screen and (max-width: 768px) {

     .horizontal-mailchimp .mc-field-group,
     .horizontal-mailchimp .clear,
     .horizontal-mailchimp input {
          display: block;
          width: 100%;
     }

     .horizontal-mailchimp .mc-field-group {
          margin-bottom: 5px;
     }
  	
}

The problem is that the changes are not saving.

I’ve tried flushing all caches and using a different browser, but this didn’t help.

I’m using Sydney theme with SiteOrigin page builder. This is the page I’m working on:

https://www.clarkandmiller.com/skype-discussion-course/

I’d really appreciate any help with this.