h(0.7 45 30)`);
    test_valid_value(`color`, `lch(from lch(0.7 45 30) l c h / alpha)`, `lch(0.7 45 30)`);
    test_valid_value(`color`, `lch(from lch(0.7 45 30 / 40%) l c h / alpha)`, `lch(0.7 45 30 / 0.4)`);
    test_valid_value(`color`, `lch(from lch(200 300 400 / 500%) l c h / alpha)`, `lch(100 300 40)`);
    test_valid_value(`color`, `lch(from lch(-200 -300 -400 / -500%) l c h / alpha)`, `lch(0 0 320 / 0)`);

    // Test nesting relative colors.
    test_valid_value(`color`, `lch(from lch(from lch(0.7 