Elixir 5.1 only produces sourcemaps for script files and none for scss and css files.

I have this simple code in my gulpfile.js file.

var elixir = require('laravel-elixir');

elixir(function(mix) {
    mix.sass('sass/style1.scss')
      .styles('css/style2.css')
      .scripts('js/script1.js');
});

But only the scripts are producing .map or sourcemap files and I don't see any errors during process. What I might have been doing wrong?