The element() CSS function defines an <image> value generated from an arbitrary HTML element. This image is live, meaning that if the HTML element is changed, the CSS properties using the resulting value are automatically updated.
The CSS linear-gradient() function creates an <image> which represents a linear gradient of colors. The result of this function is an object of the CSS <gradient> data type. Like any other gradient, a CSS linear gradient is not a CSS <color> but an image with no intrinsic dimensions; that is, it has neither natural or preferred size, nor ratio. Its concrete size will match the size of the element it applies to.
The CSS radial-gradient() function creates an <image> 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 <gradient> data type.
This works similarly to the standard radial gradients as described by radial-gradient(), but it automatically repeats the color stops infinitely in both directions, with their positions shifted by multiples of the difference between the last color stop's position and the first one's position.
The function* keyword can be used to define a generator function inside an expression.
The CSS repeating-linear-gradient function creates an <image> consisting of repeating gradients. It works similarly to the basic linear gradients as described by linear-gradient(), and takes the same arguments. However, it automatically repeats the color stops infinitely in both directions. The color stops' positions shift by multiples of the length of a basic linear gradient (the difference between the last color stops' position and the first).