Introducing the CSSLite gem
require 'domle'
require 'csslite'
s = "b {background-color: #ff3322 }"
xml = "<a><b>red</b><b2>green</b2><b>blue</b></a>"
doc = Domle.new(xml)
css = CSSLite.new s
css.propagate doc.root
puts doc.root.xml pretty: true
<a style=''> <b style='background-color:#ff3322'>red</b> <b2 style=''>green</b2> <b style='background-color:#ff3322'>blue</b> </a>
Resources
css csslite gem style stylesheet