Below are a couple of links that should be extremely helpful in filling in the blanks.
I’ve created a plugin for CSS Gradient => Figma Gradient and found them useful. In particular, the W3C documentation is really helpful and has formulas to use.
Gradients Compared between Figma, Sketch and CSS: Gradient angles in CSS, Figma & Sketch
W3C Spec for Gradients: CSS Images Module Level 3
CSS Gradient to Figma Plugin: GitHub - yagudaev/css-gradient-to-figma: Plugin to insert a CSS Gradient into Figma
Figma REST API Handle Positions to Figma Plugin Transform: Figma convert `gradientHandlePositions` to `transformGradient` and vice-versa · GitHub