CSS অ্যানিমেশন গাইড 2026: ট্রানজিশন, কীফ্রেম এবং স্ক্রোল-চালিত

/* transition: property duration timing-function delay */
.button {
  background: #0066CC;
  transform: translateY(0);
  box-shadow: 0 2px 8px rgba(0,0,0,0.1);
  transition: background 200ms ease,
              transform 150ms ease,
              box-shadow 200ms ease;
}

.button:hover {
  background: #0052A3;
  transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(0,102,204,0.3);
}

.button:active {
  transform: translateY(0);
  box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

/* Timing functions */
/* ease (default), linear, ease-in, ease-out, ease-in-out */
/* cubic-bezier(x1, y1, x2, y2) — custom curve */
.smooth { transition: transform 300ms cubic-bezier(0.16, 1, 0.3, 1); } /* ease-out-expo */
.bounce { transition: transform 300ms cubic-bezier(0.34, 1.56, 0.64, 1); } /* bounce */

/* Define the animation */
@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes pulse {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.05); }
}

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

/* Apply animations */
.hero-title {
  animation: fadeInUp 600ms ease-out both;  /* both = apply forwards and backwards fill */
}

.loading-icon {
  animation: spin 1s linear infinite;
}

.highlight {
  animation: pulse 2s ease-in-out infinite;
}

/* Stagger children animations */
.card-list .card {
  animation: fadeInUp 400ms ease-out both;
}
.card-list .card:nth-child(1) { animation-delay: 0ms; }
.card-list .card:nth-child(2) { animation-delay: 100ms; }
.card-list .card:nth-child(3) { animation-delay: 200ms; }
.card-list .card:nth-child(4) { animation-delay: 300ms; }

/* Animate elements entering the DOM */
dialog, [popover] {
  opacity: 1;
  transform: scale(1);
  transition: opacity 200ms ease, transform 200ms ease,
              display 200ms ease allow-discrete; /* allow display changes */

  /* @starting-style defines state BEFORE element appears */
  @starting-style {
    opacity: 0;
    transform: scale(0.95);
  }
}

/* Exit animation via overlay::before-close (coming soon) */
/* Currently handle with JS class toggling */

/* Animate based on scroll position — NO JavaScript needed! */

@keyframes reveal {
  from { opacity: 0; transform: translateY(30px); }
  to { opacity: 1; transform: translateY(0); }
}

.reveal-on-scroll {
  animation: reveal linear both;
  animation-timeline: view();        /* tied to element's position in viewport */
  animation-range: entry 0% entry 30%; /* animate when 0-30% of element enters */
}

/* Progress bar tied to page scroll */
.reading-progress {
  position: fixed;
  top: 0;
  left: 0;
  height: 3px;
  background: #0066CC;
  transform-origin: left;
  animation: scaleX linear;
  animation-timeline: scroll(root);   /* tied to document scroll */
}

@keyframes scaleX {
  from { transform: scaleX(0); }
  to { transform: scaleX(1); }
}

// Animate between page states or route changes
async function navigateTo(url) {
  // Start transition
  const transition = document.startViewTransition(async () => {
    // Update the DOM here
    const content = await fetchPage(url);
    document.body.innerHTML = content;
  });

  // Wait for transition complete
  await transition.finished;
}

// In Next.js / React — use experimental viewTransition
import { unstable_viewTransition as viewTransition } from 'react';

function handleNavigation() {
  viewTransition(() => {
    router.push('/new-page');
  });
}

/* CSS controls the animation */
::view-transition-old(root) {
  animation: slide-out 300ms ease-out;
}

::view-transition-new(root) {
  animation: slide-in 300ms ease-out;
}

@keyframes slide-out {
  to { transform: translateX(-100%); opacity: 0; }
}

@keyframes slide-in {
  from { transform: translateX(100%); opacity: 0; }
}

/* Per-element transitions */
.hero-image {
  view-transition-name: hero;  /* matched between pages */
}
/* Browser automatically morphs .hero-image between pages! */

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}