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Understanding ”-sd-animation: sd-fadeIn; –sd-duration: 250ms; –sd-easing: ease-in;”

These three CSS custom properties (CSS variables) form a concise, modern pattern for controlling a simple fade-in animation on an element. They separate the animation selection, duration, and timing function into reusable variables so styles stay flexible and maintainable.

What each property does

• -sd-animation: sd-fadeIn;
  Names the animation to apply. This variable typically maps to a CSS @keyframes rule (for example, sd-fadeIn) defined elsewhere in your stylesheet.

• –sd-duration: 250ms;
  Controls how long the animation runs. Using a variable allows easy adjustments across components or themes.

• –sd-easing: ease-in;
  Sets the timing function for the animation, affecting acceleration. ease-in starts slowly and speeds up toward the end.

Example usage

Define the keyframes and a utility animation rule that reads these variables:

@keyframes sd-fadeIn {from { opacity: 0; transform: translateY(6px); }  to   { opacity: 1; transform: translateY(0); }}
.sd-animated {  animation-name: var(–sd-animation);  animation-duration: var(–sd-duration, 250ms);  animation-timing-function: var(–sd-easing, ease-in);  animation-fill-mode: both;}

Apply with different values per element:

.card {  –sd-animation: sd-fadeIn;  –sd-duration: 250ms;  –sd-easing: ease-in;}.toast {  –sd-animation: sd-fadeIn;  –sd-duration: 120ms;  –sd-easing: cubic-bezier(.2, .9, .3, 1);}

Why use this pattern

• Reusability: Swap animation, duration, or easing without changing the component’s core CSS.
• Theming: Different themes can override variables globally.
• Maintainability: Centralizes animation definitions and makes tuning easier.

Tips and accessibility

• Prefer durations between 100ms–400ms for micro-interactions to feel responsive.
• Avoid excessive motion for users who prefer reduced motion—honor the media query:

@media (prefers-reduced-motion: reduce) {  .sd-animated { animation: none; transition: none; }}

• Combine opacity with subtle transform (translateY/scale) for more natural motion.

Conclusion

Using variables like -sd-animation, –sd-duration, and –sd-easing gives you a clean, flexible way to manage animations across a project. Define the keyframes once, then fine-tune behavior per component by overriding these variables.