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-sd-animation: sd-fadeIn; –sd-duration: 0ms; –sd-easing: ease-in;

This article explains the CSS custom properties shown in the title, how they affect animations, and practical usage patterns for modern web UI.

What these properties mean

  • -sd-animation: custom property naming an animation preset — here sd-fadeIn, which implies a fade-in effect (opacity from 0 → 1).
  • –sd-duration: duration of the animation; 0ms means no visible animation (instant).
  • –sd-easing: timing-function controlling acceleration; ease-in starts slow and speeds up.

Why you might see them together

Design systems often expose animation presets via CSS variables so components can opt into consistent motion. Using a preset name plus duration and easing lets designers adjust timing without changing keyframes.

Example: defining the preset

Define a keyframes rule and map the preset name to that keyframes sequence using a helper:

css
@keyframes sd-fadeIn {from { opacity: 0; transform: translateY(8px); }  to   { opacity: 1; transform: translateY(0); }}
/* default variables /:root{  –sd-animation: sd-fadeIn;  –sd-duration: 200ms;  –sd-easing: ease-out;}
/ helper to apply the animation if duration > 0 */.fade-in {  animation-name: var(–sd-animation);  animation-duration: var(–sd-duration);  animation-timing-function: var(–sd-easing);  animation-fill-mode: both;}

Handling 0ms duration

A –sd-duration: 0ms effectively disables visual motion. That can be useful for:

  • Preferring instant state changes in reduced-motion contexts.
  • During initial render where motion would feel janky.
  • Running on low-power devices or when user prefers reduced motion.

To respect users who prefer reduced motion, detect the preference and set duration to 0:

css
@media (prefers-reduced-motion: reduce) {  :root { –sd-duration: 0ms; }}

Making the preset robust

  • Provide sensible defaults in :root.
  • Allow component-level overrides for delay, iteration, and direction:
css
.modal {  –sd-duration: 240ms;  –sd-delay: 40ms;  animation-delay: var(–sd-delay, 0ms);  animation-iteration-count: 1;}
  • Ensure the keyframes include transform and opacity changes for smoother, GPU-accelerated animations.

Accessibility considerations

  • Honor prefers-reduced-motion.
  • Avoid animations that trigger vestibular disorders (large translations/rotations).
  • Use 0ms or disable animations for focus-critical interactions.

Practical examples

  • Instant state change: set –sd-duration: 0ms to show/hide UI instantly.
  • Staggered entrance: increment –sd-delay across list items to create a cascading fade-in using the same sd-fadeIn preset.
  • Theme switch: increase duration for a pronounced transition when toggling themes.

Troubleshooting

  • If animation-name appears as the literal string sd-fadeIn, ensure the keyframes name matches and the property is used in animation-name.
  • If no animation runs, check computed animation-duration — zero disables it.
  • Use will-change: opacity, transform sparingly to hint at upcoming animations for better performance.

Conclusion

Using variables like -sd-animation, –sd-duration, and –sd-easing gives design systems flexible, consistent motion control. Setting –sd-duration: 0ms is a deliberate tool to disable motion when needed — useful for accessibility, performance, or instant state changes.

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