The animation-composition property defines how multiple animations affecting the same CSS property are combined when they run at the same time. Instead of one animation simply overriding another, this property controls how their effects interact, making it possible to layer animations in a more intentional and predictable way. This is especially useful when building complex UI motion, where separate animations may control different aspects of movement, timing, or emphasis but still need to coexist without visual conflict.

Traditionally, when multiple animations targeted the same property, the result could feel limiting or unpredictable, as later animations would often override earlier ones. With animation-composition, each animation can contribute to the final computed value in a controlled manner. This allows designers and developers to think in terms of animation layers, where effects can build upon one another rather than compete. For example, a base animation might define a subtle motion, while another adds emphasis or interaction feedback, all without rewriting or duplicating logic. This makes animation systems more modular and easier to maintain over time.

The property works alongside other animation-related features, such as animation-name, which determines which animations are applied, and animation-timing-function, which defines how those animations progress over time. While those properties control what plays and how it moves, animation-composition governs how multiple animations blend together. This separation of concerns makes it easier to reason about animation behavior, especially in large projects or component-based design systems.

In practice, animation-composition is particularly valuable for modern interfaces that rely on layered motion - such as hover effects combined with attention cues or state transitions. Instead of rewriting animations or carefully timing them to avoid clashes, developers can define clear composition rules that ensure smooth and intentional motion. This leads to cleaner code, better reusability, and more expressive animations that feel cohesive rather than chaotic.