Need support for `@value` declarations

### Problem
Css modules variables values not converted by `color` function

### Example
```
// index.css
@value transparentBlack: color(#333 a(8%));
```

```
//index.js
@import { transparentBlack } from './index.css';

console.log(transparentBlack) 
```

### Intended outcome
rgba(51, 51, 51, 0.36)

### Actual outcome
color(#333 a(8%))
