var parser = require('postcss-value-parser');

/*{
    nodes: [
      type: 'function',
      value: 'rgba',
      nodes: [
        { type: 'word', value: '233' },
        { type: 'div', value: ',', before: '', after: ' ' },
        { type: 'word', value: '45' },
        { type: 'div', value: ',', before: '', after: ' ' },
        { type: 'word', value: '66' },
        { type: 'div', value: ',', before: ' ', after: '' },
        { type: 'word', value: '.5' }
      ]
    ]
  }*/
parser('rgba(233, 45, 66 ,.5)')
  .walk('rgba', function (fn) {
    var color = fn.filter(function (node) {
      return node.type === 'word';
    }); // [233, 45, 66, .5]
    fn.type = 'word';
    fn.value = convertToHex(color);
  })
  .toString();
  // #E92D42

// .2rem
{
  number: '.2',
  unit: 'rem'
}