Feature Request: relative-font-units does not report absolute units inside math functions (clamp(), calc(), min(), max())

Environment

ESLint version: v10.10.0
@eslint/css version: v2.0.0
Node version: v22.15.0
npm version: v11.12.1
Operating System: Windows 11

Which language are you using?

stylesheet

What did you do?

eslint.config.js

import css from "@eslint/css";
import { defineConfig } from "eslint/config";

export default defineConfig([
	{
		files: ["**/*.css"],
		plugins: { css },
		language: "css/css",
		rules: { "css/relative-font-units": "error" },
	},
]);

test.css

/* reported (expected) */
.a {
  font-size: 12px;
}
.b {
  font: 12px Arial;
}

/* not reported (unexpected) */
.c {
  font-size: clamp(12px, 2vw, 20px);
}
.d {
  font-size: calc(12px + 1rem);
}
.e {
  font-size: min(12px, 1rem);
}
.f {
  font: clamp(12px, 2vw, 20px) Arial;
}

npx eslint test.css

What did you expect to happen?

The 12px inside clamp(), calc(), and min() in .c–.f should be reported. The rule exists to disallow absolute font-size units, and font-size: clamp(12px, 2vw, 20px) still uses px. Fluid typography with clamp() is a very common pattern, so this is a significant gap.

What actually happened?

Only .a and .b are reported. Every declaration whose value is a math function (.c–.f) passes silently, even though each one contains 12px.

test.css
  3:14  error  Use only allowed relative units for 'font-size' - rem  css/relative-font-units
  6:9   error  Use only allowed relative units for 'font-size' - rem  css/relative-font-units

✖ 2 problems (2 errors, 0 warnings)

Link to Minimal Reproducible Example

https://stackblitz.com/edit/stackblitz-starters-8rrnybj4?file=eslint.config.js

Participation

• I am willing to submit a pull request for this issue.

AI acknowledgment

• I did not use AI to generate this issue report.
• (If the above is not checked) I have reviewed the AI-generated content before submitting.

Additional comments

No response

Disclosure: I'm a participant of open source contribution program OSSCA