## Problem
Using a negative modifier with `theme()` inside an arbitrary value
produces no CSS output.
- ✅ `ms-[theme(margin.1)]` — works
- ✅ `-ms-[10px]` — works
- ❌ `-ms-[theme(margin.1)]` — no output
## Cause
`negateValue()` in `src/util/negateValue.js` doesn't recognize `theme()`
as a negatable function. It falls through all conditions and returns
`undefined`, causing the utility to be silently dropped.
## Fix
Added `'theme'` to the `numericFunctions` list so `theme()` values get
wrapped in `calc(... * -1)`, which the PostCSS `theme()` resolver then
processes downstream.
## Tests
- **Unit test** (`negateValue.test.js`):
`negateValue('theme(margin.1)')` returns `calc(theme(margin.1) * -1)`
- **Integration test** (`arbitrary-values.test.js`):
`-mt-[theme(spacing.1)]` produces `margin-top: -0.25rem`
---------
Co-authored-by: Casey Corcoran <casecorc@amazon.com>
Co-authored-by: Robin Malfait <malfait.robin@gmail.com>
