CSS Animations – @keyframes Complete Guide

@keyframes – Defining the Motion

A @keyframes rule defines a named animation with waypoints (keyframes) that specify what CSS looks like at each point in the animation timeline.

CSS – @keyframes syntax

/* from / to — two-step animation */
@keyframes fade-in {
  from { opacity: 0; transform: translateY(12px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* Percentage waypoints — multi-step */
@keyframes bounce {
  0%   { transform: translateY(0);    }
  30%  { transform: translateY(-24px); }
  60%  { transform: translateY(-12px); }
  80%  { transform: translateY(-6px);  }
  100% { transform: translateY(0);    }
}

/* Multiple properties at once */
@keyframes hero-entrance {
  0%   { opacity: 0; transform: scale(0.8) translateY(40px); }
  60%  { opacity: 1; transform: scale(1.02) translateY(-4px); }
  100% { opacity: 1; transform: scale(1) translateY(0); }
}

/* Rules can share keyframes */
@keyframes pulse {
  0%, 100% { transform: scale(1); opacity: 1; }
  50%       { transform: scale(1.05); opacity: 0.85; }
}

▶ Live animation demos

Pulse

Fade In

The Animation Properties

animation-name

CSS

animation-name: fade-in;       /* matches @keyframes name */
animation-name: none;          /* disables animation */
animation-name: spin, pulse;   /* multiple animations */

animation-duration

CSS

animation-duration: 0.6s;    /* how long one cycle takes */
animation-duration: 1500ms;  /* same as 1.5s */

animation-timing-function

Same values as transition-timing-function: ease, linear, ease-in, ease-out, ease-in-out, cubic-bezier(), steps().

animation-delay

CSS

animation-delay: 0s;      /* starts immediately */
animation-delay: 0.5s;    /* waits 0.5s before starting */
animation-delay: -1s;     /* starts 1s INTO the animation (skip beginning) */

animation-iteration-count

CSS

animation-iteration-count: 1;         /* play once (default) */
animation-iteration-count: 3;         /* play 3 times */
animation-iteration-count: infinite;  /* loop forever */
animation-iteration-count: 2.5;       /* 2.5 cycles — ends halfway through */

animation-direction

CSS

animation-direction: normal;            /* default — plays forward */
animation-direction: reverse;           /* plays backward */
animation-direction: alternate;         /* forward, then backward, then forward… */
animation-direction: alternate-reverse; /* backward, then forward, then backward… */

animation-fill-mode

Controls what styles apply before and after the animation runs — one of the most misunderstood properties.

CSS – fill-mode

animation-fill-mode: none;      /* default — no styles held */
animation-fill-mode: forwards;  /* keep final keyframe styles after animation ends */
animation-fill-mode: backwards; /* apply from keyframe styles during delay period */
animation-fill-mode: both;      /* apply backwards + forwards — almost always what you want */

/* Example: fade-in that stays visible after finishing */
.card {
  opacity: 0;   /* start invisible */
  animation: fade-in 0.6s ease-out 0.2s both;
  /* 'both' means:
     - during delay (0.2s): apply 'from' styles (opacity: 0) — no flash of visible
     - after ending: keep 'to' styles (opacity: 1) — stays visible */
}

animation-play-state

CSS

animation-play-state: running;  /* default — animation plays */
animation-play-state: paused;   /* pause the animation */

/* Pause on hover */
.spinner:hover { animation-play-state: paused; }

/* Controlled by JS class */
.anim-paused { animation-play-state: paused; }

animation Shorthand

CSS – animation shorthand

/* animation: name duration timing-function delay iteration-count direction fill-mode */
animation: fade-in 0.6s ease-out 0.2s 1 normal both;

/* Most common shorthand patterns */
.spinner { animation: spin 0.8s linear infinite; }
.pulse   { animation: pulse 2s ease-in-out infinite; }
.entrance { animation: fade-in 0.5s ease-out both; }
.stagger  { animation: slide-up 0.4s ease-out 0.1s both; }

/* Multiple animations on one element */
.element {
  animation:
    fade-in  0.5s ease-out both,
    float    3s ease-in-out 0.5s infinite;
}

Real-World Animation Patterns

CSS – Practical animations

/* 1. Loading spinner */
@keyframes spin {
  to { transform: rotate(360deg); }
}
.spinner {
  width: 40px; height: 40px;
  border: 4px solid #e0e0e0;
  border-top-color: #1572B6;
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

/* 2. Skeleton loader (shimmer) */
@keyframes shimmer {
  0%   { background-position: -400px 0; }
  100% { background-position:  400px 0; }
}
.skeleton {
  background: linear-gradient(90deg, #e0e0e0 25%, #f5f5f5 50%, #e0e0e0 75%);
  background-size: 800px 100%;
  animation: shimmer 1.5s infinite;
  border-radius: 4px;
}

/* 3. Page entrance (stagger children) */
@keyframes slide-up {
  from { opacity: 0; transform: translateY(20px); }
  to   { opacity: 1; transform: translateY(0); }
}
.card { animation: slide-up 0.4s ease-out both; }
.card:nth-child(1) { animation-delay: 0s; }
.card:nth-child(2) { animation-delay: 0.08s; }
.card:nth-child(3) { animation-delay: 0.16s; }
.card:nth-child(4) { animation-delay: 0.24s; }

/* 4. Attention pulse */
@keyframes attention {
  0%, 100% { box-shadow: 0 0 0 0 rgba(21,114,182,0.4); }
  70%       { box-shadow: 0 0 0 12px rgba(21,114,182,0); }
}
.notification-dot { animation: attention 2s infinite; }

/* 5. Floating effect */
@keyframes float {
  0%, 100% { transform: translateY(0); }
  50%       { transform: translateY(-12px); }
}
.hero-icon { animation: float 3s ease-in-out infinite; }

/* 6. Typewriter cursor */
@keyframes blink { 0%, 100% { opacity: 1; } 50% { opacity: 0; } }
.cursor { animation: blink 1s step-end infinite; }

/* 7. Accessibility: always respect reduced motion */
@media (prefers-reduced-motion: reduce) {
  .spinner, .skeleton, .card, .notification-dot, .hero-icon, .cursor {
    animation: none;
  }
}

▶ Skeleton loader demo

📋 Summary

@keyframes name { } — defines the animation. Use from/to or percentage waypoints.
animation-name — links element to a @keyframes rule.
animation-duration — how long one cycle takes.
animation-iteration-count: infinite — loops forever.
animation-direction: alternate — forward then backward (ping-pong).
animation-fill-mode: both — apply first keyframe during delay, keep last keyframe after end. Almost always use both.
animation-play-state: paused — pause/resume with CSS or JS.
Shorthand: animation: name duration timing delay count direction fill
Stagger: use animation-delay with :nth-child().
Always add prefers-reduced-motion override.

Frequently Asked Questions

Why does my animation flash at the start? +

The element shows its natural CSS state before the animation's first keyframe applies. Fix: set animation-fill-mode: backwards or both — this applies the from keyframe styles immediately, even during the delay period. For a fade-in animation, also set opacity: 0 on the element as a backup for browsers that don't support fill-mode.

How do I restart a CSS animation? +

CSS animations don't replay once complete unless looped. To restart via JavaScript: remove the class with the animation, force a reflow (read element.offsetWidth), then re-add the class. Example: el.classList.remove('animated'); el.offsetWidth; el.classList.add('animated');. The reflow forces the browser to process the removal before re-adding, restarting the animation from the beginning.

Can I control CSS animations with JavaScript? +

Yes, several ways: (1) Toggle a CSS class that applies the animation. (2) Set animation-play-state: paused/running via element.style.animationPlayState. (3) Use the Web Animations API (element.getAnimations()) for fine-grained control — play, pause, reverse, change speed, and listen for animation events. (4) Listen to animation events: animationstart, animationend, animationiteration.