Recently some UI improvements around the Manage Jenkins page have been introduced. The visual changes are very subtle but behind them, there are interesting benefits.
Some of the goals that we have tried to achieve:
Applying a semantic HTML
Removing the <table> tag usage for implementing layouts and content structures. Read this article if you want to know reasons and/or arguments.
Small re-styling focused on spacing, margins, composition,...
JEP-200 has been integrated into Jenkins weekly builds
and (if all goes well) will be a part of the next LTS line.
In a nutshell, this change is a security hardening measure
to be less permissive about deserializing Java classes defined in the Java Platform or libraries bundled with Jenkins.
For several years now, Jenkins has specifically blacklisted certain classes and packages according to known or suspected exploits;