CSS Transition vs Animation Handbook – How to Animate Elements in CSS

CSS transitions and animations provide smooth, gradual ways to change an element's style. But they work in different ways.

Here are the main distinctions between them:

CSS Transition	CSS Animation
Creates smooth transitions from one CSS value to another. You need triggers to run CSS transitions. For instance, you can use the `:hover` pseudo-class to run transitions when a user's pointer hovers over an element. Transition has only two states: an initial and a final state. You cannot create intermediate steps. Runs only once. Best used for basic style changes.	Animates the style change from one CSS keyframe to another. CSS animations do not need triggers. Animation allows you to create multiple states. You can run multiple animation iterations—even to infinity. Best used for dynamic style changes.

This handbook uses examples to explain the two animating techniques so that you can understand their similarities and differences.

What Are CSS Transitions?
Categories of CSS Transition Properties
Shorthand for Defining the CSS Transition Properties
What is CSS Animation?
- Components of CSS Animations
- What are CSS @keyframes?
What Are CSS Animation Properties?
What is the CSS animation Property?
Important Stuff to Know about CSS Transitions and Animations
Wrapping up

Without further ado, let's discuss CSS transitions.

What Are CSS Transitions?

CSS transitions provide a smooth and gradual way to change a specific CSS property's value.

So, instead of allowing browsers to change a property's value immediately, CSS transitions cause the change to happen smoothly over a specified period of time.

For instance, suppose you wish to change an element's size on hover. In that case, you have two options:

Implement the change without CSS transitions.
Use CSS transitions to transition smoothly from the element's initial size to its new state.

Let's see some examples of the two options.

How to change an image's size on mouse hover without using CSS transitions

img {
  width: 40%;
}

img:hover {
  width: 100%;
}

Try Editing It

The code above instantaneously changes the image's size from its initial width (40%) to its new dimension (100%) because we did not use CSS transitions.

With CSS transitions, you will get a much more pleasing experience. Let's see an example below.

How to change an image's size on mouse hover with CSS transitions

img {
  width: 40%;
  transition: width 3s ease-out 0.4s;
}

img:hover {
  width: 100%;
}

Try Editing It

The transition property applied a smooth and gradual transition from width: 40% to width: 100% on the image.

Categories of CSS Transition Properties

We have two categories of CSS transition properties:

Required transition properties
Optional transition properties

Let's discuss the two.

What Are the Required CSS Transition Properties?

The two required properties you need to create CSS transitions are:

transition-property
transition-duration

What is the CSS transition-property?

The CSS transition-property specifies the CSS property you wish to transition from its initial to its new state.

What is the CSS transition-duration Property?

The CSS transition-duration property defines the length of time in which browsers should complete the selected element's transition. In other words, transition-duration sets the total start-to-finish time.

Note the following:

The transition-duration property only accepts time in milliseconds (ms) or seconds (s).
Zero seconds (0s) is the transition-duration's default value. Therefore, no transition event will occur if you do not define a transition-duration property.
transition-duration accepts only a zero (0) or a positive numeric value. Browsers will ignore the duration declaration if you provide anything else.

Examples of the Required CSS Transition Properties

Below are some examples of the two required CSS transition properties.

How to transition an element's width within three seconds

img {
  width: 40%;
  transition-property: width;
  transition-duration: 3s;
}

img:hover {
  width: 100%;
}

Try Editing It

Here's what we did in the snippet above:

The transition-property tells browsers to transition the img's width from its initial value (40%) to its new state (100%).
We used the transition-duration property to define three seconds (3s) duration from the start to the end of the transition.

Therefore, instead of an instantaneous change from the image's initial width (40%) to its new size (100%), browsers will transition smoothly between the old and new state in three seconds (3s).

How to transition a font's size within five seconds

p {
  font-size: 1rem;
  transition-property: font-size;
  transition-duration: 5s;
}

p:hover {
  font-size: 7rem;
}

Try Editing It

Here's what we did in the snippet above:

The transition-property informs browsers to transition the p element's font-size.
We used the transition-duration property to define a five-second (5s) duration from the start to the end of the transition.

Therefore, instead of an immediate change from the paragraph's initial font size (1rem) to its new size (7rem), browsers will transition smoothly between the old and new state in five seconds (5s).

Let's now discuss the optional CSS transition properties.

What Are the Optional CSS Transition Properties?

The two optional CSS transition properties are:

transition-timing-function
transition-delay

What is the CSS transition-timing-function Property?

The CSS transition-timing-function property defines the implementation timing (speed) of the selected element's transition.

In other words, the transition-timing-function specifies the speed for implementing the transition at various intervals of its duration.

The values the transition-timing-function property accepts are:

ease: Starts the transition slowly. Then, speeds it up and ends it slowly. ease is the transition-timing-function property's default value. It is equivalent to cubic-bezier(0.25,0.1,0.25,1).
ease-in: Starts the transition slowly with a gradual increase in speed. It is equal to cubic-bezier(0.42,0,1,1).
ease-out: Starts fast and ends the transition slowly. It is equivalent to cubic-bezier(0,0,0.58,1).
ease-in-out: Starts and ends the transition slowly. It is equal to cubic-bezier(0.42,0,0.58,1).
linear: Starts and ends the transition using a consistent speed throughout the transition's duration. It is equivalent to cubic-bezier(0,0,1,1).
cubic-bezier(p1, p2, p3, p4): Allows you to define the values of the cubic-bezier curve.

What is the CSS transition-delay Property?

The CSS transition-delay property defines how long the browser should wait before it starts the transition.

Note the following:

The transition-delay property must be in milliseconds (ms) or seconds (s).
0s is the transition-delay's default value. It causes the transition to start immediately from the moment browsers apply it to an HTML element.
A negative value causes the transition to begin immediately from the specified time. For instance, suppose an element's transition-delay value is -3s. In that case, the transition will start immediately at 3 seconds.
A positive value causes the transition to begin after the specified delay time has elapsed. For instance, suppose an element's transition-delay value is 3s. In that case, the transition will start after a 3-second delay.

Examples of the Optional CSS Transition Properties

Below are some examples of the two optional CSS transition properties.

How to transition an element's width with an ease-out speed

img {
  width: 40%;
  transition-property: width;
  transition-duration: 3s;
  transition-timing-function: ease-out;
}

img:hover {
  width: 100%;
}

Try Editing It

Here's what we did in the snippet above:

The transition-property informs browsers to transition the img element's width.
We used the transition-duration property to define three seconds (3s) duration from the start to the end of the transition.
We used the transition-timing-function property to begin the transition quickly and end it slowly.

How to transition an element's width with a linear speed

img {
  width: 40%;
  transition-property: width;
  transition-duration: 3s;
  transition-timing-function: linear;
}

img:hover {
  width: 100%;
}

Try Editing It

Here's what we did in the snippet above:

The transition-property informs browsers to transition the img element's width.
We used the transition-duration property to define three seconds (3s) duration from the start to the end of the transition.
The transition-timing-function property tells browsers to transition from the element's initial width to its new size using a consistent transition speed throughout.

How to transition an element's width with a two-second delay

img {
  width: 40%;
  transition-property: width;
  transition-duration: 3s;
  transition-timing-function: linear;
  transition-delay: 2s;
}

img:hover {
  width: 100%;
}

Try Editing It

Here's what we did in the snippet above:

The transition-property informs browsers to transition the img element's width property.
We used the transition-duration property to define three seconds (3s) duration from the start to the end of the transition.
The transition-timing-function property transitions the img element's width using a consistent transition speed.
We used the transition-delay property to apply a two-second (2s) delay to the starting time of the transition.

Now that we know the CSS transition properties, we can discuss defining them with a shorthand syntax.

Shorthand for Defining the CSS Transition Properties

We use the transition property as shorthand for the transition-property, transition-duration, transition-timing-function, and transition-delay properties.

In other words, instead of writing:

img {
  transition-property: width;
  transition-duration: 3s;
  transition-timing-function: linear;
  transition-delay: 2s;
}

You can alternatively use the transition property to shorten your code like so:

img {
  transition: width 3s linear 2s;
}

Try Editing It

Here is the transition property's syntax:

transition: <property-name> <duration> <timing-function> <delay>;

Note that you can use the transition property to transition the state of multiple CSS properties.

Here's an example:

img {
  width: 40%;
  opacity: 0.4;
  transition: width 3s linear, opacity 4s ease-out, transform 5s;
}

img:hover {
  width: 100%;
  opacity: 1;
  transform: rotate(45deg);
}

Try Editing It

The snippet above used commas (,) to separate each of the transitional properties we are applying to the img element.

So, now that we know what CSS transitions are and how they work, we can discuss CSS animations.

What is CSS Animation?

CSS animations provide a smooth and gradual way to animate an element's style changes from one keyframe to another.

Components of CSS Animations

CSS animations consist of two components:

Keyframes
Animation properties

What are CSS @keyframes?

@keyframes define the styles you want browsers to apply smoothly to an element at some specified key moments (frames).

Syntax of CSS @keyframes

A CSS @keyframes at-rule consists of the following:

An @keyframes keyword
The @keyframes' name
A block of zero or more keyframes
The animation's key moment selector
The key moment's style declarations

Here's an illustration:

Anatomy of CSS @keyframes at-rule A CSS @keyframes at-rule consists of a keyword, a name, and a block of keyframes

Examples of CSS @keyframes

Below are examples of the CSS @keyframes.

How to define `change-color`'s keyframes

@keyframes change-color {
  /* The first keyframe */
  0% {background-color: purple;}
  /* The last keyframe */
  100% {background-color: yellow;}
}

Here's what we did in the snippet above:

We created the @keyframes at-rule named change-color.
We defined a keyframe for browsers to apply when an associated element's animation is at its zero percent (0%) duration.
We defined a keyframe for browsers to apply when an associated element's animation is at its one hundred percent (100%) duration.

Note:

You can name your @keyframes anything you wish.
0% is equivalent to the keyword from. And 100% is the same as the keyword to. In other words, the snippet above is equal to the following:

@keyframes change-color {
  /* The first keyframe */
  from {background-color: purple;} 
  /* The last keyframe */
  to {background-color: yellow;} 
}

An animation's start and end states (from and to) are optional.
Suppose you omit an @keyframes' start (0%) or end (100%) state. In that case, browsers will default to the element's existing styles for either state.
The important rule (!important) does not work in keyframes. Browsers will ignore any keyframe declaration with an !important rule.

Let's see another example.

How to define `shape-image`'s keyframes

@keyframes shape-image {
  0% { width: 40%; border: 5px solid blue;}
  40% { width: 70%; border: 1px solid red; border-radius: 50%;}
  75% { width: 50%; border: 30px solid green;}
  100% { width: 100%; border: 7px solid purple;}
}

Here's what we did in the snippet above:

We created the @keyframes ruleset named shape-image.
We defined four keyframes for browsers to apply when an associated element's animation is at the specified key moments.

Tip: Use the CSSKeyframesRule interface in JavaScript to access the CSS @keyframes at-rules.

So, now that we know the CSS @keyframes ruleset, we can discuss the other component of CSS animations—animation properties.

What Are CSS Animation Properties?

CSS animation properties inform browsers about the animation you wish to apply to a specific element.

In other words, CSS animation properties describe the animation's attributes, such as its name, duration, direction, and iteration.

The nine (9) types of CSS animation properties are:

animation-name
animation-duration
animation-timing-function
animation-delay
animation-iteration-count
animation-direction
animation-play-state
animation-fill-mode
animation

Let's discuss each one now.

What is the CSS `animation-name` property?

The CSS animation-name property defines the name of the @keyframes at-rules containing the styles you wish to apply to a specific element.

Here's an example:

div {
  width: 150px;
  height: 150px;
  animation-name: change-color;
}

@keyframes change-color {
  from {background-color: purple;}
  to {background-color: yellow;}
}

Here's what we did in the snippet above:

The animation-name property specifies the @keyframes we wish to apply to the div element.
We created change-color's @keyframes ruleset.
We defined two keyframes for browsers to use when the div element's animation is at its zero percent (0%) and one hundred percent (100%) duration.

Tip: You can use the keyword none to deactivate an animation.

What is the CSS `animation-duration` property?

The CSS animation-duration property defines the time to complete one animation cycle.

Note the following:

The animation-duration property must be in milliseconds (ms) or seconds (s) units.
animation-duration's value must be zero or positive. Otherwise, browsers will ignore the duration declaration.
Zero seconds (0s) is animation-duration's default value.
Suppose 0s is animation-duration's value. In that case, browsers will still execute the animation by firing the animationStart and animationEnd events. But the animation-fill-mode's value will determine whether the animation is visible. For instance, if you set the animation-fill-mode to none, the animation will be invisible.

Let's see some examples of the animation-duration property.

How to animate an element's color change within three seconds

div {
  width: 150px;
  height: 150px;
  animation-name: change-color;
  animation-duration: 3s;
}

@keyframes change-color {
  from {background-color: purple;}
  to {background-color: yellow;}
}

Try Editing It

Here's what we did in the snippet above:

The animation-name property specifies the @keyframes we wish to apply to the div element.
The animation-duration property sets the animation's runtime for one cycle to three seconds (3s).
We created change-color's @keyframes ruleset.
We defined two keyframes for browsers to apply when the div element's animation is at zero percent (0%) and one hundred percent (100%) duration.

Therefore, browsers will create a smooth three-second animation from change-color's first keyframe to its last.

How to animate an image's border and width changes within seven seconds

img {
  animation-name: shape-image;
  animation-duration: 7s;
}

@keyframes shape-image {
  0% { width: 40%; border: 5px solid blue;}
  40% { width: 70%; border: 1px solid red; border-radius: 50%;}
  75% { width: 50%; border: 30px solid green;}
  100% { width: 100%; border: 7px solid purple;}
}

Try Editing It

Here's what we did in the snippet above:

The animation-name property specifies the @keyframes we wish to apply to the img element.
The animation-duration property sets the animation's runtime for one cycle to seven seconds (7s).
We created shape-image's @keyframes ruleset.
We defined four keyframes for browsers to apply when the image's animation is at the specified key moments.

Therefore, browsers will create a smooth seven-second animation from shape-image's first keyframe to its last.

What is the CSS `animation-timing-function` property?

The CSS animation-timing-function property defines an animation's implementation timing (speed) throughout its duration.

In other words, the animation-timing-function property specifies the speed for implementing the animation at various intervals of its duration.

The values the animation-timing-function property accepts are:

ease: Starts the animation slowly. Then speeds it up and ends it slowly. ease is the animation-timing-function property's default value. It is equivalent to cubic-bezier(0.25, 0.1, 0.25, 1).
ease-in: Starts the animation slowly with a gradual increase in speed. It is equivalent to cubic-bezier(0.42, 0, 1, 1).
ease-out: Starts fast and ends the animation slowly. It is equivalent to cubic-bezier(0, 0, 0.58, 1).
ease-in-out: Starts and ends the animation slowly. It is equivalent to cubic-bezier(0.42, 0, 0.58, 1).
linear: Starts and ends the animation using a consistent speed throughout the animation's duration. It is equivalent to cubic-bezier(0, 0, 1, 1).
cubic-bezier(p1, p2, p3, p4): Allows you to define the values of the cubic-Bezier curve.

Let's see some examples of the animation-timing-function property.

How to animate an element's width change using a linear speed

div {
  width: 150px;
  height: 150px;
  background-color: purple;
  animation-name: change-width;
  animation-duration: 7s;
  animation-timing-function: linear;
}

@keyframes change-width {
  from {width: 50px;}
  to {width: 100%;}
}

Try Editing It

Here's what we did in the snippet above:

The animation-name property specifies the @keyframes we wish to apply to the div element.
The animation-duration property sets the animation's runtime for one cycle to seven seconds (7s).
The linear timing function applied a consistent speed to the div's animation.
We created change-width's @keyframes ruleset.
We defined two keyframes for browsers to apply when the div's animation is at zero percent (0%) and one hundred percent (100%) duration.

Therefore, browsers will create a smooth seven-second animation from change-width's first keyframe to its last.

Let's see another example.

How to animate an element's width change using an ease-in-out and a linear speed

div {
  width: 150px;
  height: 150px;
  color: white;
  animation-name: change-width;
  animation-duration: 7s;
}

.first-div {
  background-color: purple;
  animation-timing-function: ease-in-out;
}

.second-div {
  background-color: orange;
  animation-timing-function: linear;
}

@keyframes change-width {
  from {width: 50px;}
  to {width: 100%;}
}

Try Editing It

Here's what we did in the snippet above:

The animation-name property specifies the @keyframes we wish to apply to the div element.
The animation-duration property sets the animation's runtime for one cycle to seven seconds (7s).
We used the ease-in-out timing function to apply a slow start and slow end speed to the first-div's animation.
The linear timing function applied a consistent speed to the second-div's animation.
We created change-width's @keyframes ruleset.
We defined two keyframes for browsers to apply when the div elements' animations are at their zero percent (0%) and one hundred percent (100%) durations.

Therefore, browsers will create a smooth seven-second animation from change-width's first keyframe to its last.

What is the CSS `animation-delay` property?

The CSS animation-delay property defines how long browsers should wait before starting an animation.

In other words, use animation-delay to specify whether the animation should start immediately from the beginning, immediately from a specific time, or later (after some delay).

Note the following:

The animation-delay property must be in milliseconds (ms) or seconds (s) units.
0s is animation-delay's default value. It causes the animation to start once browsers apply it to an HTML element.
A negative value causes the animation to start immediately from the specified time. For instance, suppose an element's animation-delay value is -3s. In that case, the animation will begin immediately at 3 seconds.
A positive value causes the animation to start after the specified delay time has elapsed. For instance, suppose an element's animation-delay value is 3s. In that case, the animation will begin after a 3-second delay.

Let's see some examples of the animation-delay property.

How to animate an element's width change with a four-second delay

div {
  width: 150px;
  height: 150px;
  color: white;
  animation-name: change-width;
  animation-duration: 7s;
}

.first-div {
  background-color: purple;
  animation-timing-function: ease-in-out;
}

.second-div {
  background-color: orange;
  animation-timing-function: linear;
  animation-delay: 4s;
}

@keyframes change-width {
  from {width: 50px;}
  to {width: 100%;}
}

Try Editing It

Here's what we did in the snippet above:

The animation-name property specifies the @keyframes we wish to apply to the div elements.
The animation-duration property sets the animation's runtime for one cycle to seven seconds (7s).
We used the ease-in-out timing function to apply a slow start and slow end speed to the first-div's animation.
The linear timing function applied a consistent speed to the second-div's animation.
The animation-delay property applied a four-second (4s) delay to the starting time of the second-div's animation.
We created change-width's @keyframes ruleset.
We defined two keyframes for browsers to apply when the div elements' animations are at their zero percent (0%) and one hundred percent (100%) durations.

Therefore, browsers will delay the second-div's animation for four seconds while starting the first-div's animation immediately.

Below is another example of the animation-delay property.

How to animate an element's width change from the fourth-second mark of the animation sequence

div {
  width: 150px;
  height: 150px;
  color: white;
  animation-name: change-width;
  animation-duration: 7s;
}

.first-div {
  background-color: purple;
  animation-timing-function: ease-in-out;
}

.second-div {
  background-color: orange;
  animation-timing-function: linear;
  animation-delay: -4s;
}

@keyframes change-width {
  from {width: 50px;}
  to {width: 100%;}
}

Try Editing It

Here's what we did in the snippet above:

The animation-name property specifies the @keyframes we wish to apply to the div elements.
The animation-duration property sets the animation's runtime for one cycle to seven seconds (7s).
We used the ease-in-out timing function to apply a slow start and slow end speed to the first-div's animation.
The linear timing function applied a consistent speed to the second-div's animation.
The animation-delay property makes the second-div's animation start from the fourth-second mark of the animation sequence.
We created change-width's @keyframes ruleset.
We defined two keyframes for browsers to apply when the div elements' animations are at their zero percent (0%) and one hundred percent (100%) durations.

Therefore, browsers will start the second-div's animation immediately at the fourth-second mark.

What is the CSS `animation-iteration-count` property?

The CSS animation-iteration-count property defines the number of times browsers should repeat an animation.

Note the following:

1 is animation-iteration-count's default value.
The animation-iteration-count property accepts non-integer values—for instance, 0.5 tells browsers to play half of a single animation cycle.
animation-iteration-count does not accept negative values.
An infinite value means browsers should repeat the animation forever.

Below are some examples.

How to animate an element's width change with a two-cycle iteration

div {
  width: 70px;
  height: 50px;
  background-color: purple;
  animation-name: change-width;
  animation-duration: 5s;
  animation-timing-function: ease-in-out;
  animation-iteration-count: 2;
}

@keyframes change-width {
  from {width: 70px;}
  to {width: 100%;}
}

Try Editing It

Here's what we did in the snippet above:

The animation-name property specifies the @keyframes we wish to apply to the div element.
The animation-duration property sets the animation's runtime for one cycle to five seconds (5s).
We used the ease-in-out timing function to apply a slow start and slow end speed to the div's animation.
The animation-iteration-count property tells browsers to run the animation twice.
We created change-width's @keyframes ruleset.
We defined two keyframes for browsers to apply when the div element's animation is at zero percent (0%) and one hundred percent (100%) duration.

Therefore, browsers will run the div's animation in two cycles.

Below is another example of the animation-iteration-count property.

How to animate an element's width change with an infinite iteration

div {
  width: 70px;
  height: 50px;
  animation-name: change-width;
  animation-duration: 5s;
  animation-timing-function: ease-in-out;
  animation-iteration-count: infinite;
}

@keyframes change-width {
  from {width: 70px; background-color: purple;}
  to {width: 100%; background-color: orange;}
}

Try Editing It

Here's what we did in the snippet above:

The animation-name property specifies the @keyframes we wish to apply to the div element.
The animation-duration property sets the animation's runtime for one cycle to five seconds (5s).
We used the ease-in-out timing function to apply a slow start and slow end speed to the div's animation.
The animation-iteration-count property tells browsers to run the animation infinitely.
We created change-width's @keyframes ruleset.
We defined two keyframes for browsers to apply when the div element's animation is at its zero percent (0%) and one hundred percent (100%) duration.

Therefore, browsers will run the div's animation infinitely.

What is the CSS `animation-direction` property?

The CSS animation-direction property specifies whether the animation's first iteration should run forward or backward. It also defines whether browsers should alternate the direction of subsequent iterations.

The values animation-direction accepts are:

normal: Play the animation in the normal direction (that is, forward). normal is animation-direction's default value.
reverse: Play the animation in the reverse direction (backward).
alternate: Play the first animation cycle in the normal direction. Then, alternates the subsequent iterations between the backward and forward directions.
alternate-reverse: Play the first animation cycle in the reverse direction. Then, alternates the subsequent iterations between the forward and backward directions.

Below are some examples.

How to animate an element's width change while starting each animation cycle backward

div {
  width: 70px;
  height: 50px;
  animation-name: change-width;
  animation-duration: 5s;
  animation-timing-function: ease-in-out;
  animation-iteration-count: infinite;
  animation-direction: reverse;
}

@keyframes change-width {
  from {width: 70px; background-color: purple;}
  to {width: 100%; background-color: orange;}
}

Try Editing It

Here's what we did in the snippet above:

The animation-name property specifies the @keyframes we wish to apply to the div element.
The animation-duration property sets the animation's runtime for one cycle to five seconds (5s).
We used the ease-in-out timing function to apply a slow start and slow end speed to the div's animation.
The animation-iteration-count property tells browsers to run the animation infinitely.
The animation-direction property starts each animation cycle in reverse (backward).
We created change-width's @keyframes ruleset.
We defined two keyframes for browsers to apply when the div element's animation is at zero percent (0%) and one hundred percent (100%) duration.

Below is another example of the animation-direction property.

How to animate an element's width change while alternating the animation's direction

div {
  width: 70px;
  height: 50px;
  animation-name: change-width;
  animation-duration: 5s;
  animation-timing-function: ease-in-out;
  animation-iteration-count: infinite;
  animation-direction: alternate;
}

@keyframes change-width {
  from {width: 70px; background-color: purple;}
  to {width: 100%; background-color: orange;}
}

Try Editing It

Here's what we did in the snippet above:

The animation-name property specifies the @keyframes we wish to apply to the div element.
The animation-duration property sets the animation's runtime for one cycle to five seconds (5s).
We used the ease-in-out timing function to apply a slow start and slow end speed to the div's animation.
The animation-iteration-count property tells browsers to run the animation infinitely.
The animation-direction property alternates the direction of each cycle's animation.
We created change-width's @keyframes ruleset.
We defined two keyframes for browsers to apply when the div element's animation is at zero percent (0%) and one hundred percent (100%) duration.

What is the CSS `animation-play-state` property?

The CSS animation-play-state property specifies whether the browser is running or has paused a specific animation.

The values the animation-play-state property accepts are:

running: Specifies that the browser is running the animation. running is animation-play-state's default value.
paused: Specifies that the browser has paused the animation.

Here's an example:

div {
  width: 70px;
  height: 50px;
  animation-name: change-width;
  animation-duration: 5s;
  animation-timing-function: ease-in-out;
  animation-iteration-count: infinite;
  animation-direction: alternate;
}

div:hover {
  animation-play-state: paused;
}

@keyframes change-width {
  from {width: 70px; background-color: purple;}
  to {width: 100%; background-color: orange;}
}

Try Editing It

Here's what we did in the snippet above:

The animation-name property specifies the @keyframes we wish to apply to the div element.
The animation-duration property sets the animation's runtime for one cycle to five seconds (5s).
We used the ease-in-out timing function to apply a slow start and slow end speed to the div's animation.
The animation-iteration-count property tells browsers to run the animation infinitely.
The animation-direction property alternates the direction of each cycle's animation.
We used the animation-play-state on the div's hover pseudo-class to pause the animation whenever users move their mouse over the div element.
We created change-width's @keyframes ruleset.
We defined two keyframes for browsers to apply when the div element's animation is at zero percent (0%) and one hundred percent (100%) duration.

What is the CSS `animation-fill-mode` property?

The CSS animation-fill-mode property defines the styles browsers should apply to an element before (or after) its animation runs.

The values the animation-fill-mode property accepts are:

none: Browsers will apply no style to the element before or after the animation runs. none is animation-fill-mode's default value.
forwards: The element will retain the last keyframe's style declarations when the animation ends. (Note: The animation-direction and animation-iteration-count properties determine the last keyframe.)
backwards: The element will retain the first keyframe's style declarations during the animation-delay period. (Note: The animation-direction property determines the first keyframe.)
both: Browsers will apply both the forwards and backwards rules. Therefore, the animation properties will extend in both directions.

Below are some examples.

How to style an element after its animation ends

div {
  width: 70px;
  height: 50px;
  background-color: green;
  animation-name: change-width;
  animation-duration: 5s;
  animation-timing-function: ease-in-out;
  animation-fill-mode: forwards;
}

@keyframes change-width {
  from {width: 70px; background-color: purple;}
  to {width: 100%; background-color: orange;}
}

Try Editing It

Here's what we did in the snippet above:

The animation-name property specifies the @keyframes we wish to apply to the div element.
The animation-duration property sets the animation's runtime for one cycle to five seconds (5s).
We used the ease-in-out timing function to apply a slow start and slow end speed to the div's animation.
The animation-fill-mode property tells browsers to retain the last keyframe's style declarations when the animation ends.
We created change-width's @keyframes ruleset.
We defined two keyframes for browsers to apply when the div element's animation is at zero percent (0%) and one hundred percent (100%) duration.

Below is another example of the animation-fill-mode property.

How to style an element during its animation delay period

div {
  width: 70px;
  height: 50px;
  background-color: green;
  animation-name: change-width;
  animation-duration: 5s;
  animation-timing-function: ease-in-out;
  animation-delay: 3s;
  animation-fill-mode: backwards;
}

@keyframes change-width {
  from {width: 70px; background-color: purple;}
  to {width: 100%; background-color: orange;}
}

Try Editing It

Here's what we did in the snippet above:

The animation-name property specifies the @keyframes we wish to apply to the div element.
The animation-duration property sets the animation's runtime for one cycle to five seconds (5s).
We used the ease-in-out timing function to apply a slow start and slow end speed to the div's animation.
The animation-fill-mode property tells browsers to retain the first keyframe's style declarations during the animation-delay period.
We created change-width's @keyframes ruleset.
We defined two keyframes for browsers to apply when the div element's animation is at zero percent (0%) and one hundred percent (100%) duration.

Let's see a third example of the animation-fill-mode property.

How to style an element during its animation delay and after the animation

div {
  width: 70px;
  height: 50px;
  background-color: green;
  animation-name: change-width;
  animation-duration: 5s;
  animation-timing-function: ease-in-out;
  animation-delay: 3s;
  animation-fill-mode: both;
}

@keyframes change-width {
  from {width: 70px; background-color: purple;}
  to {width: 100%; background-color: orange;}
}

Try Editing It

Here's what we did in the snippet above:

The animation-name property specifies the @keyframes we wish to apply to the div element.
The animation-duration property sets the animation's runtime for one cycle to five seconds (5s).
We used the ease-in-out timing function to apply a slow start and slow end speed to the div's animation.
The animation-fill-mode property tells browsers to apply both the forwards and backwards rules.
We created change-width's @keyframes ruleset.
We defined two keyframes for browsers to use when the div element's animation is at zero percent (0%) and one hundred percent (100%) duration.

What is the CSS `animation` Property?

We use the animation property as a shorthand for:

animation-name
animation-duration
animation-timing-function
animation-delay
animation-iteration-count
animation-direction
animation-play-state
animation-fill-mode

In other words, instead of writing:

div {
  animation-name: change-width;
  animation-duration: 5s;
  animation-timing-function: ease-in-out;
  animation-delay: 2s;
  animation-iteration-count: 3;
  animation-direction: alternate;
  animation-play-state: running;
  animation-fill-mode: both;
}

You can alternatively use the animation property to shorten your code like so:

div {
  animation: 5s ease-in-out 2s 3 alternate both running change-width;
}

Try Editing It

Here is the animation property's syntax:

animation: animation-duration animation-timing-function animation-delay animation-iteration-count animation-direction animation-fill-mode animation-play-state animation-name;

Note:

The way you arrange the time values is essential. Browsers read the first time-value as animation-duration. And they assign the second one to animation-delay.
It is best to list animation-name last. Otherwise, browsers may assign the animation-name's value to other properties.
You can apply multiple @keyframes rulesets to an element using the animation property. Here's an example:

div {
  width: 70px;
  height: 70px;
  background-color: green;
  animation: 
    5s ease-in-out 3s 3 alternate both change-width, 
    5s 3s infinite alternate both change-shape, 
    5s 3s infinite rotate-hue;
}

@keyframes change-width {
  from {width: 70px; background-color: purple;}
  to {width: 100%; background-color: orange;}
}

@keyframes change-shape {
  from {border-radius: 0%; border: 1px solid blue;}
  to {border-radius: 50%; border: 7px solid green;}
}

@keyframes rotate-hue {
  from {filter: hue-rotate(0deg);}
  to {filter: hue-rotate(360deg);}
}

Try Editing It

The snippet above applied three @keyframes rulesets to the div element using commas (,) to separate each @keyframes' configurations.

Note: We used the hue-rotate() function to rotate the div's colors.

Important Stuff to Know about CSS Transitions and Animations

You can't animate all CSS properties. Have a look at MDN's Animatable CSS properties article to see the ones you can animate.
CSS transitions and animations are expensive operations for most CSS properties—except opacity and transform. In other words, applying transitions (or animations) to any CSS box model property is inherently a CPU-intensive task. Therefore, animate only opacity, and transform properties if you are concerned about your page's performance.
Be mindful of the layout repainting issues that CSS transitions may cause through your elements' stacking order.

Wrapping up

In this article, we discuss the differences between CSS transitions and animations. We also used examples to discuss how to use them.

Thanks for reading.

And here's a useful React TypeScript resource:

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Table of Contents

What Are CSS Transitions?

How to change an image's size on mouse hover without using CSS transitions

How to change an image's size on mouse hover with CSS transitions

Categories of CSS Transition Properties

What Are the Required CSS Transition Properties?

What is the CSS transition-property?

What is the CSS transition-duration Property?

Examples of the Required CSS Transition Properties

How to transition an element's width within three seconds

How to transition a font's size within five seconds

What Are the Optional CSS Transition Properties?

What is the CSS transition-timing-function Property?

What is the CSS transition-delay Property?

Examples of the Optional CSS Transition Properties

How to transition an element's width with an ease-out speed

How to transition an element's width with a linear speed

How to transition an element's width with a two-second delay

Shorthand for Defining the CSS Transition Properties

What is CSS Animation?

Components of CSS Animations

What are CSS @keyframes?

Syntax of CSS @keyframes

Examples of CSS @keyframes

How to define change-color's keyframes

How to define shape-image's keyframes

What Are CSS Animation Properties?

What is the CSS animation-name property?

What is the CSS animation-duration property?

How to animate an element's color change within three seconds

How to animate an image's border and width changes within seven seconds

What is the CSS animation-timing-function property?

How to animate an element's width change using a linear speed

How to animate an element's width change using an ease-in-out and a linear speed

What is the CSS animation-delay property?

How to animate an element's width change with a four-second delay

How to animate an element's width change from the fourth-second mark of the animation sequence

What is the CSS animation-iteration-count property?

How to animate an element's width change with a two-cycle iteration

How to animate an element's width change with an infinite iteration

What is the CSS animation-direction property?

How to animate an element's width change while starting each animation cycle backward

How to animate an element's width change while alternating the animation's direction

What is the CSS animation-play-state property?

What is the CSS animation-fill-mode property?

How to style an element after its animation ends

How to style an element during its animation delay period

How to style an element during its animation delay and after the animation

What is the CSS animation Property?

Important Stuff to Know about CSS Transitions and Animations

Wrapping up

And here's a useful React TypeScript resource:

How to define `change-color`'s keyframes

How to define `shape-image`'s keyframes

What is the CSS `animation-name` property?

What is the CSS `animation-duration` property?

What is the CSS `animation-timing-function` property?

What is the CSS `animation-delay` property?

What is the CSS `animation-iteration-count` property?

What is the CSS `animation-direction` property?

What is the CSS `animation-play-state` property?

What is the CSS `animation-fill-mode` property?

What is the CSS `animation` Property?