• Chapter 9 — CSS Animations & Transitions
  • Part 1 — Transitions
    • Without vs With Transition
    • Transition Syntax
    • Common Transitions
  • transform — Moving and Reshaping Elements
  • Part 2 — Keyframe Animations
    • Defining with @keyframes
    • Applying an Animation
    • Common Animations
    • Staggered Animations
    • Performance — What to Animate
    • Always Respect User Preferences

§Chapter 9 — CSS Animations & Transitions

§Part 1 — Transitions

A transition says: “When this property changes, move smoothly over time instead of jumping instantly.”

§Without vs With Transition

/* Without — instant jump */
.button { background: blue; }
.button:hover { background: red; }

/* With — smooth change */
.button {
  background: blue;
  transition: background 300ms ease;
}
.button:hover { background: red; }

§Transition Syntax

transition: property duration timing-function delay;
transition: background-color 300ms ease 0ms;

duration — how long: 200ms, 0.5s

timing-function:

Multiple properties:

.card {
  transition:
    background-color 300ms ease,
    transform 200ms ease-out,
    box-shadow 300ms ease;
}

§Common Transitions

Hover lift:

.card {
  transform: translateY(0);
  box-shadow: 0 2px 8px rgba(0,0,0,0.1);
  transition: transform 200ms ease-out, box-shadow 200ms ease-out;
}
.card:hover {
  transform: translateY(-6px);
  box-shadow: 0 12px 24px rgba(0,0,0,0.15);
}

Button press:

.button {
  transform: scale(1);
  transition: transform 100ms ease, opacity 100ms ease;
}
.button:hover  { opacity: 0.9; }
.button:active { transform: scale(0.96); }

§transform — Moving and Reshaping Elements

transform is GPU-accelerated — silky smooth and doesn’t affect layout.

transform: translateX(100px);      /* move right */
transform: translateY(-20px);      /* move up */
transform: translate(50px, -20px); /* move right AND up */
transform: scale(1.1);             /* 10% bigger */
transform: scale(0.9);             /* 10% smaller */
transform: rotate(45deg);          /* rotate clockwise */
transform: rotate(-90deg);         /* counter-clockwise */
transform: skewX(10deg);           /* slant */

/* Combine multiple */
transform: translateY(-6px) scale(1.02) rotate(2deg);

💡 Always prefer animating transform and opacity over width, height, margin, or top/left.

§Part 2 — Keyframe Animations

Transitions are A→B. Animations are A→B→C→D→… They can loop and run automatically.

§Defining with @keyframes

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(20px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* Or with percentage steps */
@keyframes pulse {
  0%   { transform: scale(1); }
  50%  { transform: scale(1.05); }
  100% { transform: scale(1); }
}

§Applying an Animation

.card {
  animation: fadeIn 500ms ease forwards;
}

All animation properties:

.element {
  animation-name:            fadeIn;
  animation-duration:        500ms;
  animation-timing-function: ease;
  animation-delay:           200ms;
  animation-iteration-count: infinite;  /* or a number */
  animation-direction:       alternate; /* normal, reverse, alternate */
  animation-fill-mode:       forwards;  /* none, forwards, backwards, both */
  animation-play-state:      running;   /* running or paused */
}

/* Shorthand */
animation: fadeIn 500ms ease 200ms infinite alternate forwards;

§Common Animations

Spinning loader:

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

.loader {
  width: 40px;
  height: 40px;
  border: 4px solid #e5e7eb;
  border-top-color: #2563eb;
  border-radius: 50%;
  animation: spin 700ms linear infinite;
}

Bounce:

@keyframes bounce {
  0%, 100% { transform: translateY(0); }
  50%       { transform: translateY(-20px); }
}

.arrow { animation: bounce 1s infinite; }

Slide in:

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

§Staggered Animations

Cards appear one after another:

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(20px); }
  to   { opacity: 1; transform: translateY(0); }
}

.card {
  opacity: 0;
  animation: fadeUp 400ms ease-out forwards;
}

.card:nth-child(1) { animation-delay: 0ms; }
.card:nth-child(2) { animation-delay: 100ms; }
.card:nth-child(3) { animation-delay: 200ms; }
.card:nth-child(4) { animation-delay: 300ms; }

§Performance — What to Animate

/* ✅ FAST — GPU accelerated */
transform: translate(), scale(), rotate()
opacity

/* ⚠️ SLOW — causes layout reflow */
width, height, margin, padding, top, left

§Always Respect User Preferences

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

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