Animations Skill

This skill guides the creation of beautiful, purposeful animations using CSS and Svelte's built-in transition system. Great animations feel natural, add delight, and improve user experience.

When to Use This Skill

•Adding hover states and micro-interactions
•Creating page transitions
•Animating elements on scroll
•Building loading states and skeletons
•Creating staggered list animations
•Adding entrance animations to sections
•Building interactive UI elements

Philosophy

Animations should be:

•Purposeful - Every animation communicates something
•Subtle - Enhancement, not distraction
•Fast - Users shouldn't wait for animations
•Consistent - Same timing and easing throughout

Avoid:

•Animations that block user action
•Motion for motion's sake
•Jarring or unexpected movements
•Inconsistent timing across the site

Timing & Easing Reference

Standard Durations

Type	Duration	Use Case
Micro	100-150ms	Button hovers, icon changes
Fast	200-300ms	Fade ins, small movements
Medium	300-500ms	Page elements, cards
Slow	500-800ms	Page transitions, large elements

Recommended Easings

css

/* Smooth and natural */
--ease-out: cubic-bezier(0.33, 1, 0.68, 1);

/* Snappy entrance */
--ease-out-back: cubic-bezier(0.34, 1.56, 0.64, 1);

/* Elegant deceleration */
--ease-out-expo: cubic-bezier(0.16, 1, 0.3, 1);

Svelte Transitions

Built-in Transitions

svelte

<script lang="ts">
	import { fade, fly, slide, scale, blur } from 'svelte/transition';

	let visible = $state(true);
</script>

{#if visible}
	<div transition:fade={{ duration: 300 }}>Fades in and out</div>
{/if}

Common Transition Patterns

Fade In

svelte

{#if visible}
	<div in:fade={{ duration: 300, delay: 0 }}>Content</div>
{/if}

Fly Up

svelte

{#if visible}
	<div in:fly={{ y: 20, duration: 400 }}>Content slides up</div>
{/if}

Scale In

svelte

{#if visible}
	<div in:scale={{ start: 0.95, duration: 300 }}>Content scales in</div>
{/if}

Custom Transitions

svelte

<script lang="ts">
	import { cubicOut } from 'svelte/easing';

	function customFly(node: HTMLElement, { delay = 0, duration = 400 }) {
		return {
			delay,
			duration,
			easing: cubicOut,
			css: (t: number) => `
        transform: translateY(${(1 - t) * 20}px);
        opacity: ${t};
      `
		};
	}
</script>

{#if visible}
	<div in:customFly={{ duration: 400 }}>Custom animation</div>
{/if}

CSS Animation Patterns

Hover Scale

svelte

<button class="hover:scale-[1.02] active:scale-[0.98] transition-transform duration-150">
	Click me
</button>

Fade Up on Mount (CSS)

svelte

<div class="fade-up">Content</div>

<style>
	.fade-up {
		animation: fadeUp 0.5s cubic-bezier(0.33, 1, 0.68, 1) forwards;
	}

	@keyframes fadeUp {
		from {
			opacity: 0;
			transform: translateY(20px);
		}
		to {
			opacity: 1;
			transform: translateY(0);
		}
	}
</style>

Staggered Children (CSS)

svelte

<ul>
	{#each items as item, i}
		<li class="stagger-item" style="animation-delay: {i * 100}ms">
			{item}
		</li>
	{/each}
</ul>

<style>
	.stagger-item {
		opacity: 0;
		animation: fadeUp 0.4s cubic-bezier(0.33, 1, 0.68, 1) forwards;
	}

	.stagger-item:nth-child(1) {
		animation-delay: 0ms;
	}
	.stagger-item:nth-child(2) {
		animation-delay: 100ms;
	}
	.stagger-item:nth-child(3) {
		animation-delay: 200ms;
	}
	.stagger-item:nth-child(4) {
		animation-delay: 300ms;
	}

	@keyframes fadeUp {
		from {
			opacity: 0;
			transform: translateY(20px);
		}
		to {
			opacity: 1;
			transform: translateY(0);
		}
	}
</style>

Loading Skeleton

svelte

<div class="h-4 bg-gray-200 rounded skeleton"></div>

<style>
	.skeleton {
		animation: pulse 1.5s ease-in-out infinite;
	}

	@keyframes pulse {
		0%,
		100% {
			opacity: 0.5;
		}
		50% {
			opacity: 1;
		}
	}
</style>

Scroll-Triggered Animations

Using Intersection Observer

svelte

<script lang="ts">
	import { onMount } from 'svelte';

	let element: HTMLElement;
	let isVisible = $state(false);

	onMount(() => {
		const observer = new IntersectionObserver(
			(entries) => {
				entries.forEach((entry) => {
					if (entry.isIntersecting) {
						isVisible = true;
						observer.unobserve(entry.target);
					}
				});
			},
			{ threshold: 0.1, rootMargin: '-50px' }
		);

		observer.observe(element);

		return () => observer.disconnect();
	});
</script>

<section
	bind:this={element}
	class="transition-all duration-500 ease-out {isVisible
		? 'opacity-100 translate-y-0'
		: 'opacity-0 translate-y-8'}"
>
	Content appears on scroll
</section>

Reusable InView Component

svelte

<!-- src/lib/components/InView.svelte -->
<script lang="ts">
	import { onMount } from 'svelte';
	import { browser } from '$app/environment';

	interface Props {
		children: import('svelte').Snippet;
		threshold?: number;
		rootMargin?: string;
		once?: boolean;
	}

	let { children, threshold = 0.1, rootMargin = '-50px', once = true }: Props = $props();

	let element: HTMLElement;
	let isVisible = $state(false);
	let prefersReducedMotion = $state(false);

	onMount(() => {
		// Respect user's motion preferences
		prefersReducedMotion = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

		if (prefersReducedMotion) {
			isVisible = true;
			return;
		}

		const observer = new IntersectionObserver(
			(entries) => {
				entries.forEach((entry) => {
					if (entry.isIntersecting) {
						isVisible = true;
						if (once) observer.unobserve(entry.target);
					} else if (!once) {
						isVisible = false;
					}
				});
			},
			{ threshold, rootMargin }
		);

		observer.observe(element);
		return () => observer.disconnect();
	});
</script>

<div
	bind:this={element}
	class="transition-all duration-500 ease-out {isVisible
		? 'opacity-100 translate-y-0'
		: 'opacity-0 translate-y-6'}"
>
	{@render children()}
</div>

Page Transitions

Using SvelteKit's Navigation

Version Requirement: The $app/state module requires SvelteKit 2.12+. For earlier versions, use $app/stores with the $page store instead.

svelte

<!-- src/routes/+layout.svelte -->
<script lang="ts">
	import { page } from '$app/state';
	import { fade } from 'svelte/transition';

	let { children } = $props();
</script>

{#key page.url.pathname}
	<div in:fade={{ duration: 200, delay: 200 }} out:fade={{ duration: 200 }}>
		{@render children()}
	</div>
{/key}

Note: In SvelteKit 2.12+, use $app/state instead of $app/stores. The page object is reactive without needing the $page store prefix.

Performance Tips

•

Prefer transform and opacity - These are GPU-accelerated:

css

/* Good */
transform: translateX(10px);
opacity: 0.5;

/* Avoid */
left: 10px;
width: 100px;

•

Use will-change sparingly:

css

.animated-element {
	will-change: transform;
}

•

Respect reduced motion:

css

@media (prefers-reduced-motion: reduce) {
	* {
		animation-duration: 0.01ms !important;
		transition-duration: 0.01ms !important;
	}
}

•
Avoid animating on scroll without throttling - Use Intersection Observer with once: true.

Checklist Before Shipping

• Animations are fast (under 500ms for most)
• Consistent easing across the site
• Respects prefers-reduced-motion
• No layout shifts during animation
• Mobile performance tested
• Exit animations added where needed
• Stagger delays feel natural, not too slow