What problem does this address?

Currently Gutenberg restricts spacing, sizing and other dimensional controls to a fixed set of units, typically px, rem, em, %, vh and vw. This limits the freedom to use CSS like calc(), clamp() and var(). Other builders like Elementor and Divi support flexible unit input:

What is your proposed solution?

Enable free-text CSS value input alongside the unit dropdown so developers can enter any valid CSS expression. This improves flexibility for modern responsive design.