Twofold
Twofold, Cool blue: a dark duotone gradient with palette #071526, #386ba8, #d7efff. Uses native CSS gradient functions. Free for personal and commercial use.
Use with a class
Link once in your HTML head. Add these classes to your element.
More duotone gradients
How to use CSS gradients
Counterpoint
counterpoint-02
Colour field
colour-field-03