Conditional Formatting w/ RubyXL

conditional_formatting.rb

workbook = RubyXL::Workbook.new
worksheet = workbook.worksheets[0]

# Style to highlight red
style = RubyXL::DXF.new
style.font = RubyXL::Font.new
style.font.color = RubyXL::Color.new("FF0000")

# Add style to workbook
workbook.stylesheet.dxfs ||= RubyXL::DXFs.new # This was my initial problem
workbook.stylesheet.dxfs << style
style_id = workbook.stylesheet.dxfs.index(style) # need to reference this later

# Rule to highlight negative numbers
rule = RubyXL::ConditionalFormattingRule.new
rule.dxf_id = style_id
rule.type = :cellIs
rule.operator = :lessThan
rule.priority = 1
rule.formulas << RubyXL::Formula.new(expression: "0")

range = "A3:A10" # area to apply the rule
formatting = RubyXL::ConditionalFormatting.new(sgref: range)
formatting.cf_rule << rule

worksheet.conditional_formatting << formatting