Convert camel cased property names to dash separated.

@param {Object} style
@return {Object}
function convertCase(style) {
  const converted = {}

  for (const prop in style) {
    const key = prop.indexOf('--') === 0 ? prop : hyphenate(prop)

    converted[key] = style[prop]
  }

  if (style.fallbacks) {
    if (Array.isArray(style.fallbacks)) converted.fallbacks = style.fallbacks.map(convertCase)
    else converted.fallbacks = convertCase(style.fallbacks)
  }

  return converted
}