To apply a drop shadow effect on an element in CSS, you would use the “box-shadow” property. The box-shadow property attaches one or more shadows to an element.
It has the following syntax:
```
box-shadow: h-offset v-offset blur-radius spread-radius color;
```
- h-offset: sets the horizontal offset of the shadow. If positive, the shadow will be on the right of the box, if negative, it will be on the left.
- v-offset: sets the vertical offset of the shadow. If positive, the shadow will be below the box, if negative, above.
- blur-radius: define the blur radius of the shadow. The higher the number, the more blurred the shadow will be.
- spread-radius: optional. If positive, it will increase the size of the box shadow; if negative, it will decrease it.
- color: sets the color of the shadow.
An example:
```
element {
box-shadow: 5px 5px 10px rgba(0,0,0,0.5);
}
```
This will apply a shadow that is displaced 5 pixels to the right and 5 pixels down from the element. The shadow is slightly blurred (10 pixels blur radius). The color of the shadow is black with 50% transparency.
