Collapsible: --radix-collapsible-content-height CSS variable missing when equal to 0

[fuma-nama]

Bug report

Current Behavior

When the Collapsible Content height is zero (empty content), --radix-collapsible-content-height isn't added to CSS variables.
This is problematic because in CSS, variables are inherited from parents.

In a nested structure of collapsible, this causes animation that depends on --radix-collapsible-content-height to use the value from parent, which is an incorrect value.

Directory.animation.bug.mov

For example, math item is a collapsible with zero height, it inherits the variable --radix-collapsible-content-height from parent, because it is missing on the math item itself.

Expected behavior

--radix-collapsible-content-height should be defined on the content node (--radix-collapsible-content-height: 0 in element styles)

Reproducible example

https://codesandbox.io/p/sandbox/lucid-rain-wr283c

The nested item with empty content doesn't have the variable defined.

Suggested solution

N/A

Additional context

N/A

Your environment

Software	Name(s)	Version
Radix Package(s)	@radix-ui/react-collapsible	1.1.0
React	n/a	18.3.0
Browser	chrome	latest
Assistive tech
Node	n/a	18
npm/yarn	pnpm	9.5
Operating System	MacOS	14.5