How to implement animation in a mobile or web application?

In mobile and web applications, animation is implemented using specialized frameworks and APIs that allow properties of interface elements to change over time.

On iOS, animations often use UIView.animate, Core Animation, or SwiftUI with its animation modifiers. For example, a smooth change in transparency:

UIView.animate(withDuration: 0.5) {
    myView.alpha = 0.0
}

On the web, animations are achieved through CSS (properties transition and animation) or JavaScript (for example, using the GSAP library or Web Animations API). An example of CSS animation:

.my-element {
  transition: opacity 0.5s ease-in-out;
}
.my-element.hidden {
  opacity: 0;
}

Or using JavaScript:

document.querySelector('.my-element').classList.add('hidden');

The main idea is to smoothly change properties (position, size, color, transparency, etc.) over time to create a movement or transition effect.