A gradients value allows you to create gradients effect without having to make actual image file.
It is no special property, you need to use background property and define gradients values to make linear gradients and radial gradients.
You can make three different methods to different gradients effects.
Fading two colors from top side and bottom side
background: linear-gradient(red, yellow);
One side color fading
background: linear-gradient(to right, red, yellow);
background: linear-gradient(to bottom right, red, yellow);
background: linear-gradient(20dge, orange, red);
In this gradients effect one color starting from a central point and fading to another color.
background: radial-gradient (green,blue);
When you need to fade effect in shape.
background: radial-gradient (circle, green, blue);
If you want to create gradients from some specific side.
background: radial-gradient (at top left, green, blue);