As title.
CSS has a property, background-image, which you can set as a gradient with its value, linear-gradient. The usage is as follows:
background-image: linear-gradient(direction, color-stop1, color-stop2, ...) ;
The first parameter, direction, can specify, to top/bottom/right, etc., or a fixed Angle, such as 90deg. When we specify an Angle, how do we understand that Angle? Without further ado, go straight to the image above (click on the image for more details) :