When a CSS animation does not play, the browser is usually doing exactly what the CSS says, but one required piece is missing or overridden. The most common problems are a missing duration, a keyframe name mismatch, a rule with higher specificity, or reduced-motion CSS disabling the animation.
Debug animations by checking the complete chain: the selector matches the element, animation-name matches @keyframes exactly, duration is greater than zero, the element is visible, and no later rule sets animation: none or animation-play-state: paused.
Add one worked example that compares the normal path with the boundary case for CSS Animation Not Playing.
Keep the note tied to a real CSS workflow so the idea is easier to recall later.
CSS Animation Not Playing should be studied as a practical CSS lesson, not as a label. Start by naming the input, the rule that changes the input, and the result a learner should be able to predict after reading the page.
CSS animations require several properties to work together correctly. When an animation doesn't play, it's usually due to a missing animation-duration, a typo in the animation-name that doesn't match the @keyframes name, or the animation being paused.
/* ❌ Problem "" missing duration */
.element { animation: fadeIn; } /* Duration defaults to 0s! */
/* ✅ Solution "" always include duration */
.element {
animation: fadeIn 1s ease-in-out;
/* name | duration | timing | (optional: delay, iteration, direction) */
}
@keyframes fadeIn {
from { opacity: 0; }
to { opacity: 1; }
}/* ❌ Name mismatch */
.element { animation: fade-in 1s; } /* "fade-in" */
@keyframes fadeIn { /* "fadeIn" "" different! */
from { opacity: 0; }
to { opacity: 1; }
}/* ✅ Names must match exactly (case-sensitive) */
.element { animation: fadeIn 1s ease; }
@keyframes fadeIn { /* Exact match */
from { opacity: 0; }
to { opacity: 1; }
}/* ✅ Loop animation infinitely */
.spinner {
animation: spin 1s linear infinite; /* infinite = loop forever */
}
/* ✅ Keep final state after animation */
.element {
animation: slideIn 0.5s ease forwards; /* forwards = keep end state */
}
/* ✅ Alternate direction */
.pulse {
animation: pulse 1s ease-in-out infinite alternate;
/* alternate = plays forward then backward */
}/* ✅ Respect user's motion preference */
.animated {
animation: bounce 0.5s infinite;
}
@media (prefers-reduced-motion: reduce) {
.animated {
animation: none; /* Disable for users who prefer less motion */
}
}
/* ✅ Or use a subtle alternative */
@media (prefers-reduced-motion: reduce) {
.animated {
animation-duration: 0.01ms; /* Effectively instant */
}
}/* ✅ Complete animation with all properties */
.notification {
animation-name: slideDown;
animation-duration: 0.4s;
animation-timing-function: ease-out;
animation-delay: 0.1s;
animation-iteration-count: 1;
animation-direction: normal;
animation-fill-mode: forwards;
animation-play-state: running;
/* Shorthand: name duration timing delay count direction fill-mode */
animation: slideDown 0.4s ease-out 0.1s 1 normal forwards;
}
@keyframes slideDown {
from { transform: translateY(-100%); opacity: 0; }
to { transform: translateY(0); opacity: 1; }
}CSS Animation Not Playing matters in CSS because it changes how a program is written, tested, or debugged. The page should explain the normal flow first: what the developer writes, what the runtime or platform does, and what result should appear.
When teaching CSS Animation Not Playing, avoid stopping at syntax. Show the surrounding decision: why this feature is chosen, what problem it removes, and what would become harder if the feature were not used.
The strongest notes for CSS Animation Not Playing explain where the idea stops working. Add cases for missing input, wrong order, incompatible types, duplicate values, empty collections, failed requests, or configuration mismatch when those cases fit the lesson.
Readers should leave the page knowing how to inspect a bad result. For CSS Animation Not Playing, that means checking the relevant value, state, dependency, selector, query, route, class, or runtime message before changing code randomly.
.lesson-box {
display: block;
max-width: 42rem;
padding: 1rem;
}.lesson-box:empty::before {
content: "CSS Animation Not Playing: add visible content";
}Memorizing CSS Animation Not Playing without the situation where it is useful.
Connect CSS Animation Not Playing to a concrete CSS task.
Testing CSS Animation Not Playing only with the perfect input.
Include empty, missing, duplicate, incompatible, or failed cases when relevant.
Changing code before reading the visible symptom or error message.
Inspect the output, state, configuration, or stack trace connected to CSS Animation Not Playing.
Memorizing CSS Animation Not Playing without the situation where it is useful.
Connect CSS Animation Not Playing to a concrete CSS task.
Most common causes: missing animation-duration (defaults to 0s), typo in animation-name that doesn't match @keyframes, or animation-play-state: paused.
Add animation-iteration-count: infinite, or use the shorthand: animation: myAnim 1s linear infinite.
Use animation-fill-mode: forwards. This keeps the element in the state defined by the last keyframe after the animation completes.
It's a media query that detects if the user has requested reduced motion in their OS settings. Always provide a no-animation fallback for accessibility.
transform and opacity are the most performant "" they're GPU-accelerated and don't trigger layout reflow. Avoid animating width, height, margin, or padding as they cause expensive reflows.
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