The `WP_Customize_Custom_CSS_Setting::value()` method now returns the `default` if `wp_get_custom_css()` returns empty. Props westonruter, afercia, helen. See #35395. Fixes #38685. Built from https://develop.svn.wordpress.org/trunk@39151 git-svn-id: http://core.svn.wordpress.org/trunk@39091 1a063a9b-81f0-0310-95a4-ce76da25c4cd