Using the CSS gem

require 'css'

style = "body { background: #FFF url('image.png') no-repeat; }"
css = CSS::Parser.new.parse(style)
puts css['body'].background.color.to_s #=> #FFF
css['body'].background.position = 'top center'
puts css['body'].to_s #=> 'background: #FFF url('image.png') top center no-repeat'

Resources