3.8: Transitions & Animations

1. CSS Transitions

Transitions create smooth changes between CSS property values.

Basic Transition

/* Before */
.button {
  background: #42b883;
  transition: background 0.3s;
}

/* After (on hover) */
.button:hover {
  background: #35a372;
}
/* Result: Color smoothly transitions over 0.3 seconds */

Transition Properties

.element {
  /* transition: property duration timing-function delay */
  transition: background 0.3s ease-in-out 0s;

  /* Individual properties */
  transition-property: background;
  transition-duration: 0.3s;
  transition-timing-function: ease-in-out;
  transition-delay: 0s;
}

Multiple Transitions

.button {
  transition:
    background 0.3s ease,
    transform 0.2s ease,
    box-shadow 0.3s ease;
}

.button:hover {
  background: #35a372;
  transform: translateY(-2px);
  box-shadow: 0 4px 8px rgba(0,0,0,0.2);
}

Transition All

/* Transition all animatable properties */
.element {
  transition: all 0.3s ease;
}

/* ⚠️ Can impact performance - be specific when possible */

2. Timing Functions

Control the acceleration curve of transitions.

Built-in Timing Functions

.element {
  /* Linear - constant speed */
  transition: all 0.3s linear;

  /* Ease (default) - slow start, fast middle, slow end */
  transition: all 0.3s ease;

  /* Ease-in - slow start */
  transition: all 0.3s ease-in;

  /* Ease-out - slow end */
  transition: all 0.3s ease-out;

  /* Ease-in-out - slow start and end */
  transition: all 0.3s ease-in-out;
}

Cubic Bezier (Custom Curves)

.element {
  /* cubic-bezier(x1, y1, x2, y2) */
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);

  /* Material Design standard */
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);

  /* Bounce effect */
  transition: all 0.5s cubic-bezier(0.68, -0.55, 0.265, 1.55);
}

Tools: cubic-bezier.com

Steps Function

/* Stepped animation */
.element {
  transition: all 1s steps(4); /* 4 discrete steps */
  transition: all 1s steps(10, start);
  transition: all 1s steps(10, end);
}

/* Typewriter effect */
.typewriter {
  width: 0;
  overflow: hidden;
  white-space: nowrap;
  transition: width 2s steps(20);
}

.typewriter.active {
  width: 100%;
}

3. Transform Property

Move, scale, rotate, or skew elements.

2D Transforms

/* Translate (move) */
.element {
  transform: translateX(50px);      /* Move right 50px */
  transform: translateY(-20px);     /* Move up 20px */
  transform: translate(50px, -20px); /* Both X and Y */
}

/* Scale (resize) */
.element {
  transform: scale(1.5);            /* 150% size */
  transform: scaleX(0.5);           /* 50% width */
  transform: scaleY(2);             /* 200% height */
  transform: scale(1.2, 0.8);       /* Width 120%, height 80% */
}

/* Rotate */
.element {
  transform: rotate(45deg);         /* 45 degrees clockwise */
  transform: rotate(-90deg);        /* 90 degrees counter-clockwise */
}

/* Skew */
.element {
  transform: skewX(10deg);          /* Tilt horizontally */
  transform: skewY(5deg);           /* Tilt vertically */
  transform: skew(10deg, 5deg);     /* Both */
}

Multiple Transforms

/* Combine transforms (order matters!) */
.element {
  transform: translateX(100px) rotate(45deg) scale(1.5);
}

/* ⚠️ Later transforms affect earlier ones */

Transform Origin

/* Change the pivot point */
.element {
  transform-origin: center;         /* Default */
  transform-origin: top left;
  transform-origin: 50% 50%;
  transform-origin: 100px 50px;
}

/* Rotate around top-left corner */
.card {
  transform-origin: top left;
  transition: transform 0.3s;
}

.card:hover {
  transform: rotate(5deg);
}

4. CSS Animations

Create multi-step animations using keyframes.

Basic Animation

/* Define keyframes */
@keyframes slide-in {
  from {
    transform: translateX(-100%);
    opacity: 0;
  }
  to {
    transform: translateX(0);
    opacity: 1;
  }
}

/* Apply animation */
.element {
  animation: slide-in 0.5s ease-out;
}

Keyframe Percentages

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

.element {
  animation: bounce 1s ease-in-out;
}

Animation Properties

.element {
  /* animation: name duration timing-function delay iteration-count direction fill-mode */
  animation: slide-in 1s ease-out 0s 1 normal forwards;

  /* Individual properties */
  animation-name: slide-in;
  animation-duration: 1s;
  animation-timing-function: ease-out;
  animation-delay: 0s;
  animation-iteration-count: 1;        /* or infinite */
  animation-direction: normal;          /* or reverse, alternate, alternate-reverse */
  animation-fill-mode: forwards;        /* or backwards, both, none */
  animation-play-state: running;        /* or paused */
}

Iteration Count

/* Run once */
.element {
  animation: fade-in 1s 1;
}

/* Run 3 times */
.element {
  animation: pulse 0.5s 3;
}

/* Run forever */
.element {
  animation: rotate 2s infinite;
}

Animation Direction

/* Normal - start to end */
.element {
  animation: slide-in 1s normal;
}

/* Reverse - end to start */
.element {
  animation: slide-out 1s reverse;
}

/* Alternate - forward then backward */
.element {
  animation: pulse 1s infinite alternate;
}

/* Alternate-reverse - backward then forward */
.element {
  animation: pulse 1s infinite alternate-reverse;
}

Fill Mode

/* None - returns to original state */
.element {
  animation: fade-in 1s none;
}

/* Forwards - stays at end state */
.element {
  animation: fade-in 1s forwards;
}

/* Backwards - starts at first keyframe */
.element {
  animation: fade-in 1s backwards;
}

/* Both - combines forwards and backwards */
.element {
  animation: fade-in 1s both;
}

5. Common Animation Patterns

Fade In

@keyframes fade-in {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}

.element {
  animation: fade-in 0.5s ease-in;
}

Slide In

@keyframes slide-in-left {
  from {
    transform: translateX(-100%);
  }
  to {
    transform: translateX(0);
  }
}

.element {
  animation: slide-in-left 0.5s ease-out;
}

Bounce

@keyframes bounce {
  0%, 100% {
    transform: translateY(0);
  }
  50% {
    transform: translateY(-30px);
  }
}

.element {
  animation: bounce 0.5s ease-in-out;
}

Pulse

@keyframes pulse {
  0%, 100% {
    transform: scale(1);
  }
  50% {
    transform: scale(1.1);
  }
}

.button {
  animation: pulse 1s infinite;
}

Shake

@keyframes shake {
  0%, 100% { transform: translateX(0); }
  10%, 30%, 50%, 70%, 90% { transform: translateX(-10px); }
  20%, 40%, 60%, 80% { transform: translateX(10px); }
}

.error {
  animation: shake 0.5s ease-in-out;
}

Rotate

@keyframes rotate {
  from {
    transform: rotate(0deg);
  }
  to {
    transform: rotate(360deg);
  }
}

.spinner {
  animation: rotate 1s linear infinite;
}

Loading Spinner

@keyframes spin {
  to {
    transform: rotate(360deg);
  }
}

.spinner {
  width: 40px;
  height: 40px;
  border: 4px solid #f3f3f3;
  border-top: 4px solid #42b883;
  border-radius: 50%;
  animation: spin 1s linear infinite;
}

6. Hover Effects

Button Hover

.button {
  background: #42b883;
  color: white;
  padding: 12px 24px;
  border: none;
  border-radius: 4px;
  cursor: pointer;
  transition: all 0.3s ease;
}

.button:hover {
  background: #35a372;
  transform: translateY(-2px);
  box-shadow: 0 4px 8px rgba(0,0,0,0.2);
}

.button:active {
  transform: translateY(0);
  box-shadow: 0 2px 4px rgba(0,0,0,0.2);
}

Card Hover

.card {
  transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.card:hover {
  transform: translateY(-8px);
  box-shadow: 0 12px 24px rgba(0,0,0,0.15);
}

Image Zoom

.image-container {
  overflow: hidden;
}

.image-container img {
  transition: transform 0.3s ease;
}

.image-container:hover img {
  transform: scale(1.1);
}

Underline Animation

.link {
  position: relative;
  text-decoration: none;
  color: #42b883;
}

.link::after {
  content: '';
  position: absolute;
  bottom: -2px;
  left: 0;
  width: 0;
  height: 2px;
  background: #42b883;
  transition: width 0.3s ease;
}

.link:hover::after {
  width: 100%;
}

7. Performance Optimization

GPU-Accelerated Properties

Fast (use these for animations):

• transform
• opacity

/* Good - GPU accelerated */
.element {
  transition: transform 0.3s, opacity 0.3s;
}

.element:hover {
  transform: translateX(10px);
  opacity: 0.8;
}

Slow (avoid animating these):

• width, height
• top, left, right, bottom
• margin, padding

/* Bad - causes repaints */
.element {
  transition: width 0.3s;
}

.element:hover {
  width: 300px;
}

/* Good - use transform instead */
.element {
  transition: transform 0.3s;
}

.element:hover {
  transform: scaleX(1.5);
}

Will-Change

Hint to browser to optimize for animation.

/* Use sparingly - only for elements that will animate */
.element {
  will-change: transform, opacity;
}

/* Remove after animation */
.element.animated {
  will-change: transform;
  animation: slide-in 0.5s;
}

.element.animation-complete {
  will-change: auto;
}

Reduce Motion

Respect user preferences for reduced motion.

/* Respect prefers-reduced-motion */
@media (prefers-reduced-motion: reduce) {
  * {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

/* Or disable entirely */
@media (prefers-reduced-motion: reduce) {
  * {
    animation: none !important;
    transition: none !important;
  }
}

8. Practical Examples

Loading Skeleton

@keyframes loading {
  0% {
    background-position: -200px 0;
  }
  100% {
    background-position: calc(200px + 100%) 0;
  }
}

.skeleton {
  background: linear-gradient(
    90deg,
    #f0f0f0 0px,
    #e0e0e0 40px,
    #f0f0f0 80px
  );
  background-size: 200px 100%;
  animation: loading 1.2s ease-in-out infinite;
}

Progress Bar

@keyframes progress {
  from {
    width: 0%;
  }
  to {
    width: 100%;
  }
}

.progress-bar {
  width: 0%;
  height: 4px;
  background: #42b883;
  animation: progress 2s ease-out forwards;
}

Notification Slide In

@keyframes slide-in-right {
  from {
    transform: translateX(100%);
    opacity: 0;
  }
  to {
    transform: translateX(0);
    opacity: 1;
  }
}

.notification {
  position: fixed;
  top: 20px;
  right: 20px;
  animation: slide-in-right 0.5s ease-out;
}

Flip Card

.card-container {
  perspective: 1000px;
}

.card {
  transition: transform 0.6s;
  transform-style: preserve-3d;
}

.card-container:hover .card {
  transform: rotateY(180deg);
}

.card-front,
.card-back {
  backface-visibility: hidden;
}

.card-back {
  transform: rotateY(180deg);
}

9. Practical Exercises

Exercise 3.8.1: Button Interactions

Create buttons with:

• Smooth background color change
• Lift effect on hover
• Press effect on click
• Ripple animation

Exercise 3.8.2: Loading Animations

Build 3 loading spinners:

• Rotating circle
• Bouncing dots
• Skeleton screen

Exercise 3.8.3: Card Animations

Create animated cards that:

• Lift on hover
• Flip to show back
• Slide in on page load
• Stagger animation for grid

Exercise 3.8.4: Navigation Transitions

Build a menu with:

• Slide-in animation
• Underline hover effect
• Active state animation
• Mobile hamburger toggle

10. Knowledge Check

Question 1: What's the difference between transition and animation?

Question 2: Which properties are GPU-accelerated?

Question 3: What does animation-fill-mode: forwards do?

Question 4: How do you create an infinite animation?

Question 5: Why use transform instead of left/top?

Question 6: How do you respect reduced motion preferences?

11. Common Mistakes to Avoid

❌ Animating Expensive Properties

/* Bad */
.element {
  transition: width 0.3s;
}

/* Good */
.element {
  transition: transform 0.3s;
}

❌ Forgetting Transform Origin

/* Rotates from center (might look odd) */
.element {
  transform: rotate(45deg);
}

/* Rotates from top-left corner */
.element {
  transform-origin: top left;
  transform: rotate(45deg);
}

❌ Too Many Simultaneous Animations

/* Bad - performance issues */
.element {
  animation: rotate 1s infinite,
             pulse 1s infinite,
             bounce 1s infinite,
             shake 1s infinite;
}

12. Key Takeaways

✅ Transitions - Smooth changes between states ✅ Animations - Multi-step keyframe animations ✅ Transform - GPU-accelerated movement, scaling, rotation ✅ Timing functions - Control animation curves ✅ Performance - Use transform and opacity ✅ Fill mode - Control animation end state ✅ Iteration count - Run once, multiple, or infinite ✅ Accessibility - Respect prefers-reduced-motion ✅ Will-change - Optimize for animation (use sparingly) ✅ Transform origin - Control rotation/scale pivot point

13. Further Resources

Documentation:

• MDN Transitions
• MDN Animations

Tools:

• Cubic Bezier Generator
• Animista - Animation library

Inspiration:

• CodePen
• CSS Animation Examples

Next Steps

Fantastic! You can now create engaging animations and smooth interactions.

In Lesson 3.9: CSS Best Practices, you'll learn to write maintainable, scalable, and professional CSS.