[ENHANCEMENT] Add gradient option similar to Fenix

[axeltrinidade]

linear-gradient(90deg, #9400FF, #ba00e5, #df06b9, #e62da7, #f13b95, #f64d86, #f85f7a, #fc7169, #f9845b, #e8ab52)

[GangstaPichu]

This would be cool. I wish it had a way to make a rainbow progress bar.