4.1 Enhancements
- #21627 Filter for custom-background CSS selector [punt, use case is rare]
- #29949 Customizer collapsed mode is barely usable [punt, mobile first]
- #28650 Allow Customizer elements (controls, sections, and panels) to be deep-linked [needs-patch, margin bug]
- #28542 Navigating within Customizer preview should update parent document title [commit 28542.2.diff]
- #28504 Icons for Customizer Sections [punt, mobile first]
- #28032 Headers, Backgrounds, and Widgets in the Customizer are not discoverable from their separate admin screens.