UBS has been updated to WordPress 4.9.5
UBS Stewards have removed the My Custom CSS plugin from availability in favor of the newly introduced Aditional CSS functionality offered as part of WordPress Core.
From WordPress.org: https://codex.wordpress.org/CSS#Custom_CSS_in_WordPress
If you have been using the My Custom CSS Plugin to input your own CSS, these changes have been retained and moved into Customize > Additional CSS. From this interface, you can continue to input your cust CSS stylings with the added benefit of real-time preview capability offered in the Customize menu.
UBS has been updated to WordPress 4.9.4.