HashWithCssStyleKeys is solely for being able to access a hash which has css-style keys (e.g. ‘font-size’) with the underscore symbol version @example

  opts = {'font-size' => '23px', :color => 'white'}
  opts = HashWithCssStyleKeys[opts]
  opts[:font_size]   # ===> '23px'
  opts[:color]       # ===> 'white'