The first parameter is the horizontal offset of the shadow.

The second parameter is the vertical offset.

You can put negative values to place the shadow on the opposite side of the box.

The third value, always positive, is the length of the gradient.

A fourth value, not used in the demo, extends the shadow in the opposite direction.

A color code gives the color of the shadow.

The inset parameter, not used in the demo, create a shadow inside the box and not outside like this.