wp-includes/class-wp-customize-widgets.php:1283Inserts default style for highlighted widget at early point so theme stylesheet can override.
public function print_preview_css() { ?> <style> .widget-customizer-highlighted-widget { outline: none; -webkit-box-shadow: 0 0 2px rgba(30, 140, 190, 0.8); box-shadow: 0 0 2px rgba(30, 140, 190, 0.8); position: relative; z-index: 1; } </style> <?php }Introduced in 3.9.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-customize-widgets.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.