[css] Color picker for css variables

<!-- ⚠️⚠️ Do Not Delete This! feature_request_template ⚠️⚠️ --> <!-- Please read our Rules of Conduct: https://opensource.microsoft.com/codeofconduct/ --> <!-- Please search existing issues to avoid creating duplicates. --> <!-- Describe the feature you'd like. --> Currently vs code color picker doesn't display color picker on hover for a color picker where css variable is used. E.g. ```css color: hsl(0, 0%, 0%) ``` ^Works But, ```css --hue-color: 250 color: hsl(var(--hue-color), 0%, 0%) ``` ^Doesn't work. Is there a way to make it work? If the feature is not implemented is there any challenge to do so. I am currently looking at the code how this can be implemented but if some can direct me where to start would be great.