function cls(str = '', prefix = '') {
  if (str.charAt(0) === '.') {
    return `.${CSS_PREFIX}${prefix}${str.slice(1)}`;
  }

  return `${CSS_PREFIX}${prefix}${str}`;
}
Make class name for ui
@param {String} str  - main string of className
@param {String} prefix - prefix string of className
@returns {String} class name