class Sanitize::CSS

def at_rule!(rule)
  name = rule[:name].downcase
  return nil unless @config[:at_rules].include?(name)
  if AT_RULES_WITH_STYLES.include?(name)
    styles = Crass::Parser.parse_rules(rule[:block][:value],
      :preserve_comments => @config[:allow_comments],
      :preserve_hacks    => @config[:allow_hacks])
    rule[:block][:value] = tree!(styles)
  elsif AT_RULES_WITH_PROPERTIES.include?(name)
    props = Crass::Parser.parse_properties(rule[:block][:value],
      :preserve_comments => @config[:allow_comments],
      :preserve_hacks    => @config[:allow_hacks])
    rule[:block][:value] = tree!(props)
  else
    rule.delete(:block)
  end
  rule
end