Remove CSS custom properties

Author: sabernhardt

src/wp-includes/css/wp-embed-template.css

@@ -217,7 +217,7 @@ p.wp-embed-heading {
 
 .wp-embed-share-dialog-open:focus .dashicons,
 .wp-embed-share-dialog-close:focus .dashicons {
-	box-shadow: 0 0 0 var(--wp-admin-border-width-focus, 1.5px) var(--wp-admin-theme-color, #3858e9);
+	box-shadow: 0 0 0 1.5px #3858e9;
 	/* Only visible in Windows High Contrast mode */
 	outline: 2px solid transparent;
 	border-radius: 100%;