Radial gradients are defined by their center, the ending shape contour and position, and color stops. The radial gradient consists, going from its center to its ending shape and potentially beyond, of successive uniformly-scaled concentric shapes, identical to the ending shape. Color stops are positioned on a virtual gradient ray going out horizontally of the center to the right. Percentages positioning of color stops are relative to the intersection between the ending shape and this gradient ray representing 100%. Each shape is monocolor and defined by the color on the gradient ray it intersects.
Link: radial-gradient() – CSS | MDN
The CSS radial-gradient() function creates an which represents a gradient of colors radiating from an origin, the center of the gradient. The result of this function is an object of the CSS