Introduction to CSS Transitions and Animations

CSS transitions and animations are powerful tools that allow you to create engaging and dynamic user interfaces by adding visual effects to web elements. They breathe life into static content, making websites feel more responsive and interactive.

Transitions provide a smooth change in property values over a specified duration when a CSS property changes (e.g., on hover). Animations, on the other hand, provide more granular control, allowing you to create complex sequences of property changes over time, using keyframes to define different states of the animation.

By using transitions and animations judiciously, you can significantly enhance the user experience by providing visual feedback, guiding the user's attention, and making interactions feel more natural. This leads to increased user engagement and a more enjoyable browsing experience.

A Foundational Overview

At their core, CSS transitions and animations serve the same fundamental purpose: to smoothly change the appearance of an element over a period of time.

CSS Transitions

Transitions are ideal for simple, state-based changes. You define which CSS properties should transition, the duration of the transition, and the timing function (e.g., `ease`, `linear`, `ease-in-out`). They are triggered by events like `:hover`, `:focus`, or changes applied through JavaScript.

Key Transition Properties:

• transition-property: Specifies which CSS property or properties should be animated during the transition. Use `all` to animate all animatable properties.
• transition-duration: Specifies the length of time a transition animation should take to complete. Expressed in seconds (s) or milliseconds (ms).
• transition-timing-function: Specifies the speed curve of the transition effect. Values include `linear`, `ease`, `ease-in`, `ease-out`, `ease-in-out`, and `cubic-bezier()`.
• transition-delay: Specifies a delay (in seconds or milliseconds) before the transition effect starts.

Example: The blue box below changes color and width on hover using a CSS transition.

CSS Animations

Animations offer far greater control than transitions. They use the @keyframes rule to define a sequence of styles that an element will transition through over time. You can control the number of iterations, the direction, and other aspects of the animation.

Key Animation Properties:

• animation-name: Specifies the name of the @keyframes animation to be used.
• animation-duration: Specifies the length of time an animation should take to complete one cycle. Expressed in seconds (s) or milliseconds (ms).
• animation-timing-function: Specifies the speed curve of the animation effect. Values include `linear`, `ease`, `ease-in`, `ease-out`, `ease-in-out`, and `cubic-bezier()`.
• animation-delay: Specifies a delay (in seconds or milliseconds) before the animation starts.
• animation-iteration-count: Specifies the number of times an animation should be played. Use `infinite` for continuous looping.
• animation-direction: Specifies whether the animation should play forwards, backwards, or in alternating cycles. Values include `normal`, `reverse`, `alternate`, and `alternate-reverse`.
• animation-fill-mode: Specifies a style for the element when the animation is not playing (before it starts, after it ends, or both). Values include `none`, `forwards`, `backwards`, and `both`.
• animation-play-state: Specifies whether the animation is running or paused.

Example: The text below fades in using a CSS animation defined with keyframes.

This text will fade in.