You can animate a box shadow in CSS by using keyframe animations.
Here is how you might create a flickering shadow effect:
```
@keyframes flicker {
0% {box-shadow: 0 0 10px #ff0000;}
50% {box-shadow: 0 0 20px #ff0000, 0 0 30px #ff0000;}
100% {box-shadow: 0 0 10px #ff0000;}
}
.myElement {
animation: flicker 1s infinite;
}
```
This would cause the element with class “myElement” to constantly animate between a 10px and 30px red shadow, creating a flickering effect.
The `@keyframes` rule specifies the animation code. Inside it, `0%`, `50%` and `100%` specifies the state of the animation at different points in time. `0%` is the start of the animation, `100%` is the end. The percentage, or ‘keyframe’, when the animation should change to the new style, you can use as many keyframes as you like.
The animation property is a shorthand property for the following properties:
- animation-name
- animation-duration
- animation-timing-function
- animation-delay
- animation-iteration-count
- animation-direction
In this case, `flicker 1s` is the name of the animation, and `infinite` means it will repeat indefinitely. `1s` is the duration of one cycle of the animation.
Remember to include vendor prefixes (like `-webkit-`, `-moz-`, etc.) if you want the animation to work on multiple browsers.
