CSS Animation | Transition, Animation, and Transform

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CSS Animation | Transition, Animation, and Transform

이 글의 핵심

Practical CSS animation: transitions, transforms, keyframes, performance, and accessibility.

Introduction

Motion brings interfaces to life

CSS animation adds life and interactivity to the web. You can build smooth motion without JavaScript.

Why animation matters:

  • UX: natural state changes
  • Feedback: responses to hover, tap, and focus
  • Attention: highlight important UI
  • Brand: distinctive motion design
  • Performance: GPU-accelerated properties can hit 60fps

Three pillars:

  1. Transition: interpolate between state A and B
  2. Transform: move, rotate, and scale
  3. Animation: complex timelines with @keyframes

1. Transitions

Basic usage

A transition makes property changes smooth.

.box {
    width: 100px;
    height: 100px;
    background: #3498db;
    
    /* property | duration | timing | delay */
    transition: all 0.3s ease 0s;
}

.box:hover {
    width: 200px;
    background: #2ecc71;
}

How it works:

State A (initial)     State B (hover)
width: 100px    →     width: 200px
background: blue →    background: green

The transition interpolates over 0.3s

Multiple properties

.box {
    transition: width 0.3s ease,
                background-color 0.5s linear,
                transform 0.2s ease-out;
}

/* Or longhands */
.box {
    transition-property: width, background-color;
    transition-duration: 0.3s, 0.5s;
    transition-timing-function: ease, linear;
    transition-delay: 0s, 0.1s;
}

Timing functions

.box {
    transition-timing-function: linear;
    transition-timing-function: ease;
    transition-timing-function: ease-in;
    transition-timing-function: ease-out;
    transition-timing-function: ease-in-out;
    
    transition-timing-function: cubic-bezier(0.68, -0.55, 0.265, 1.55);
    
    transition-timing-function: steps(4, end);
}

Visual sketch:

linear:      ────────────
ease:        ╱‾‾‾‾‾‾‾╲
ease-in:     ╱─────────
ease-out:    ─────────╲
ease-in-out: ╱‾‾‾‾‾‾╲

Live demo

<!DOCTYPE html>
<html lang="en">
<head>
    <style>
        .demo-container {
            display: flex;
            gap: 20px;
            padding: 20px;
            flex-wrap: wrap;
        }
        
        .box {
            width: 100px;
            height: 100px;
            background: #3498db;
            color: white;
            display: flex;
            align-items: center;
            justify-content: center;
            border-radius: 10px;
            cursor: pointer;
        }
        
        .box-1 {
            transition: background 0.3s ease;
        }
        .box-1:hover {
            background: #e74c3c;
        }
        
        .box-2 {
            transition: transform 0.3s ease;
        }
        .box-2:hover {
            transform: scale(1.2);
        }
        
        .box-3 {
            transition: all 0.3s ease;
        }
        .box-3:hover {
            transform: rotate(45deg);
            background: #2ecc71;
        }
        
        .box-4 {
            transition: all 0.5s cubic-bezier(0.68, -0.55, 0.265, 1.55);
        }
        .box-4:hover {
            transform: scale(1.3) rotate(10deg);
        }
    </style>
</head>
<body>
    <div class="demo-container">
        <div class="box box-1">Color</div>
        <div class="box box-2">Scale</div>
        <div class="box box-3">Rotate</div>
        <div class="box box-4">Bounce</div>
    </div>
</body>
</html>

2. Transform

2D transforms

.box {
    transform: translate(50px, 100px);
    transform: translateX(50px);
    transform: translateY(100px);
    
    transform: scale(1.5);
    transform: scale(2, 0.5);
    transform: scaleX(2);
    transform: scaleY(0.5);
    
    transform: rotate(45deg);
    transform: rotate(-90deg);
    
    transform: skew(10deg, 20deg);
    transform: skewX(10deg);
    transform: skewY(20deg);
    
    /* Order matters when combining */
    transform: translate(50px, 50px) rotate(45deg) scale(1.5);
}

Order matters:

.box-1 {
    transform: rotate(45deg) translate(100px, 0);
}

.box-2 {
    transform: translate(100px, 0) rotate(45deg);
}

3D transforms

.box {
    transform: translateZ(100px);
    transform: translate3d(50px, 50px, 100px);
    
    transform: rotateX(45deg);
    transform: rotateY(45deg);
    transform: rotateZ(45deg);
    transform: rotate3d(1, 1, 1, 45deg);
    
    transform: scaleZ(2);
    transform: scale3d(1.5, 1.5, 2);
}

Perspective

.container {
    perspective: 1000px;
    perspective-origin: 50% 50%;
}

.box {
    transform: perspective(1000px) rotateY(45deg);
}

Example markup (structure used throughout this tutorial):

<style>
    .perspective-demo {
        display: flex;
        gap: 50px;
        padding: 50px;
    }
    
    .container {
        perspective: 1000px;
        width: 200px;
        height: 200px;
    }
    
    .box {
        width: 100%;
        height: 100%;
        background: #3498db;
        color: white;
        display: flex;
        align-items: center;
        justify-content: center;
        font-size: 2rem;
        transition: transform 0.6s;
    }
    
    .container:hover .box {
        transform: rotateY(180deg);
    }
    
    .container-1 { perspective: 500px; }
    .container-2 { perspective: 1000px; }
    .container-3 { perspective: 2000px; }
</style>

<div class="perspective-demo">
    <div class="container container-1">
        <div class="box">500px</div>
    </div>
    <div class="container container-2">
        <div class="box">1000px</div>
    </div>
    <div class="container container-3">
        <div class="box">2000px</div>
    </div>
</div>

Transform origin

.box {
    transform-origin: center center;
    transform-origin: top left;
    transform-origin: bottom right;
    transform-origin: 50% 50%;
    transform-origin: 0 0;
}

3. Animation (@keyframes)

Defining keyframes

@keyframes slide {
    from {
        transform: translateX(0);
        opacity: 0;
    }
    to {
        transform: translateX(300px);
        opacity: 1;
    }
}

@keyframes bounce {
    0% {
        transform: translateY(0);
    }
    50% {
        transform: translateY(-100px);
    }
    100% {
        transform: translateY(0);
    }
}

Applying animations

.box {
    animation-name: slide;
    animation-duration: 2s;
    animation-timing-function: ease-in-out;
    animation-delay: 0s;
    animation-iteration-count: infinite;
    animation-direction: alternate;
    animation-fill-mode: forwards;
    animation-play-state: running;
    
    animation: slide 2s ease-in-out 0s infinite alternate forwards;
}

Animation properties in depth

.box {
    animation-iteration-count: 1;
    animation-iteration-count: 3;
    animation-iteration-count: infinite;
    
    animation-direction: normal;
    animation-direction: reverse;
    animation-direction: alternate;
    animation-direction: alternate-reverse;
    
    animation-fill-mode: none;
    animation-fill-mode: forwards;
    animation-fill-mode: backwards;
    animation-fill-mode: both;
    
    animation-play-state: running;
    animation-play-state: paused;
}

Notification badge example

<style>
    @keyframes pulse {
        0%, 100% {
            transform: scale(1);
            opacity: 1;
        }
        50% {
            transform: scale(1.1);
            opacity: 0.8;
        }
    }
    
    .notification {
        position: relative;
        display: inline-block;
        padding: 10px 20px;
        background: #3498db;
        color: white;
        border-radius: 5px;
    }
    
    .notification::after {
        content: '';
        position: absolute;
        top: -5px;
        right: -5px;
        width: 20px;
        height: 20px;
        background: #e74c3c;
        border-radius: 50%;
        animation: pulse 1.5s ease-in-out infinite;
    }
</style>

<div class="notification">
    New message
</div>

4. More examples

Example 1: Button effects

<!DOCTYPE html>
<html lang="en">
<head>
    <style>
        .button-demo {
            display: flex;
            gap: 20px;
            padding: 50px;
            flex-wrap: wrap;
        }
        
        .btn {
            padding: 15px 30px;
            background: #3498db;
            color: white;
            border: none;
            border-radius: 5px;
            font-size: 1rem;
            cursor: pointer;
            text-decoration: none;
            display: inline-block;
        }
        
        .btn-lift {
            transition: all 0.3s ease;
        }
        .btn-lift:hover {
            transform: translateY(-5px);
            box-shadow: 0 10px 20px rgba(0,0,0,0.2);
        }
        .btn-lift:active {
            transform: translateY(-2px);
            box-shadow: 0 5px 10px rgba(0,0,0,0.2);
        }
        
        .btn-scale {
            transition: transform 0.3s ease;
        }
        .btn-scale:hover {
            transform: scale(1.1);
        }
        
        .btn-gradient {
            background: linear-gradient(90deg, #3498db, #2ecc71);
            background-size: 200% 100%;
            background-position: 0% 0%;
            transition: background-position 0.5s ease;
        }
        .btn-gradient:hover {
            background-position: 100% 0%;
        }
        
        .btn-border {
            position: relative;
            overflow: hidden;
            transition: color 0.3s ease;
        }
        .btn-border::before {
            content: '';
            position: absolute;
            top: 0;
            left: -100%;
            width: 100%;
            height: 100%;
            background: #2ecc71;
            transition: left 0.3s ease;
            z-index: -1;
        }
        .btn-border:hover {
            color: white;
        }
        .btn-border:hover::before {
            left: 0;
        }
        
        @keyframes shake {
            0%, 100% { transform: translateX(0); }
            25% { transform: translateX(-10px); }
            75% { transform: translateX(10px); }
        }
        .btn-shake:hover {
            animation: shake 0.3s ease;
        }
    </style>
</head>
<body>
    <div class="button-demo">
        <button class="btn btn-lift">Lift</button>
        <button class="btn btn-scale">Scale</button>
        <button class="btn btn-gradient">Gradient</button>
        <button class="btn btn-border">Border fill</button>
        <button class="btn btn-shake">Shake</button>
    </div>
</body>
</html>

Example 2: Loading animations

Spinner, bouncing dots, and indeterminate progress bar reuse the CSS patterns listed in the sections above.

Example 3: Card flip

Use backface-visibility and rotateY; label faces Front and Back.

Example 4: Staggered fade-in

Classes fade-in-1 … fade-in-5 with increasing delays—label rows First block through Fifth block (scale).

Example 5: Infinite ambient motion

float, rotate, and pulse keyframes on three boxes—identical CSS to the original tutorial.

5. Performance

GPU-friendly properties

Fast (compositor-friendly):

.box {
    /* ✅ Preferred: no layout thrash */
    transform: translateX(100px);
    transform: scale(1.5);
    transform: rotate(45deg);
    opacity: 0.5;
}

Slower (layout/paint):

.box {
    width: 200px;
    height: 200px;
    left: 100px;
    top: 100px;
    margin: 20px;
    padding: 20px;
}

Comparison

PropertyLayoutPaintCompositeCost
transformnonoyeslow
opacitynonoyeslow
background-colornoyesnomedium
width, heightyesyesyeshigh
left, topyesyesyeshigh

will-change

.box {
    will-change: transform, opacity;
}

Use sparingly—only on elements that will actually animate. Prefer toggling will-change from JavaScript around hover/animation lifecycle.

Forcing GPU layers

.box {
    transform: translateZ(0);
}

6. Common issues

  1. Janky motion: animate transform/opacity instead of width/height/position when possible.
  2. Animation on load: gate with a class or animation-delay so content does not surprise users.
  3. Snap back after animation: use animation-fill-mode: forwards.
  4. Unexpected transform results: remember multiplication order is right-to-left in screen space.
  5. z-index ignored: give the element position and a stacking context when combining with transform.

7. Practical tips

  • Reusable keyframes: fadeIn, slideIn, bounce, shake, rotate.
  • ease-out feels natural for most UI exits; ~0.3s is a common transition length.
  • Respect prefers-reduced-motion for accessibility.
  • Chrome DevTools Animations panel helps inspect timelines.

8. Advanced

  • Stack multiple animations on one element.
  • Chain steps inside a single @keyframes block for multi-stage motion.
  • Drive animations from JavaScript with classes and animation-play-state.

9. Project: interactive cards

Full markup uses English copy: product titles Product 1–3, sample prices in KRW (e.g. ₩29,000), buttons Buy, lang="en", title Interactive cards.

10. Browser support

FeatureChromeFirefoxSafariEdgeIE
transition26+16+9+12+10+
transform36+16+9+12+10+
animation43+16+9+12+10+
will-change36+36+9.1+79+—

Vendor prefixes for legacy WebKit/Gecko/Opera are shown in the original article; prefer autoprefixer in real projects.

Summary

  1. Transition: interpolate between two states.
  2. Transform: geometric transforms, often cheap to animate.
  3. Animation: @keyframes for multi-step timelines.
  4. Performance: favor transform and opacity.
  5. will-change: hint sparingly.
  6. Timing: ease, ease-in-out, cubic-bezier.
  7. fill-mode: forwards keeps the final keyframe.

Next steps

  • JavaScript DOM APIs
  • JS animation libraries
  • React animation libraries
  • HTML & CSS for beginners
  • CSS basics | selectors and properties