svelte-border-beam

Animated border beam effect for Svelte 5. A lightweight component that adds a traveling or breathing glow animation around any element - cards, buttons, inputs, or search bars.

This is a Svelte port of border-beam by Jakub Antalik. All of the visual design and the effect engine are his work - see the original repo and live demo. This package reimplements the React component wrapper with Svelte 5 runes and reuses his framework-agnostic CSS engine. Full attribution in CREDITS.md.

Install

npm install svelte-border-beam

Requires Svelte 5.

Quick start

<script>
  import { BorderBeam } from 'svelte-border-beam';
</script>

<BorderBeam>
  <div style="padding: 32px; border-radius: 16px; background: #1d1d1d;">
    Your content here
  </div>
</BorderBeam>

The component wraps your content and overlays the animated beam effect. It auto-detects the border-radius of the first child element. Anything you nest inside <BorderBeam> is passed as its children snippet.

Types

Built-in presets control the glow style and motion. They fall into two families.

Rotate (traveling beam)

<BorderBeam size="md"><Card /></BorderBeam>   <!-- Full border glow (default) -->
<BorderBeam size="sm"><IconButton /></BorderBeam>  <!-- Compact glow for small elements -->
<BorderBeam size="line"><SearchBar /></BorderBeam> <!-- Bottom-only traveling glow -->

Pulse (breathing glow, no rotation)

<BorderBeam size="pulse-inner"><Card /></BorderBeam>   <!-- Contained breathing border glow -->
<BorderBeam size="pulse-outside"><Card /></BorderBeam> <!-- Outward-blooming halo around the element -->

Both pulse types support all color variants, strength, theme, and the breathe speed via duration (defaults to 2.3).

pulse-outside requires an opaque wrapped child. The colorful core and halo render behind your content and bloom outward, so only the part that spills beyond the element shows. If your child is transparent, the inner glow will show through. The wrapper uses overflow: visible, so make sure the surrounding layout has room for the halo to spill.

pulse-outside relies on the wrapped element's own 1px border as the idle hairline. It does not paint its own hairline by default. If your child has no border, add a subtle 1px border (or box-shadow: inset 0 0 0 1px) so the edge stays defined while the beam is faded out.

Color variants

<BorderBeam colorVariant="colorful" /> <!-- Rainbow spectrum (default) -->
<BorderBeam colorVariant="mono" />     <!-- Grayscale -->
<BorderBeam colorVariant="ocean" />    <!-- Blue-purple tones -->
<BorderBeam colorVariant="sunset" />   <!-- Orange-yellow-red tones -->

All variants except mono animate through a hue-shift cycle.

Theme

Adapts beam colors for dark or light backgrounds:

<BorderBeam theme="dark" />  <!-- Dark background (default) -->
<BorderBeam theme="light" /> <!-- Light background -->
<BorderBeam theme="auto" />  <!-- Detects system preference -->

Strength

Control the overall intensity of the effect without affecting the wrapped content:

<BorderBeam strength={0.7}><Card /></BorderBeam> <!-- 70% intensity -->

strength accepts a value from 0 (invisible) to 1 (full intensity, default).

Play / pause

Toggle the animation on and off with smooth fade transitions:

<script>
  import { BorderBeam } from 'svelte-border-beam';
  let active = $state(true);
</script>

<button onclick={() => (active = !active)}>Toggle</button>

<BorderBeam {active} onDeactivate={() => console.log('faded out')}>
  <Card />
</BorderBeam>

Props

| Prop | Type | Default | Description | |------|------|---------|-------------| | children | Snippet | - | Content to wrap (nested content is used automatically) | | size | 'sm' \| 'md' \| 'line' \| 'pulse-outside' \| 'pulse-inner' | 'md' | Size/type preset | | colorVariant | 'colorful' \| 'mono' \| 'ocean' \| 'sunset' | 'colorful' | Color palette | | theme | 'dark' \| 'light' \| 'auto' | 'dark' | Background adaptation | | strength | number | 1 | Effect opacity (0-1), only affects the beam layers | | duration | number | 1.96 / 3.1 / 2.3 | Animation cycle duration in seconds (rotate / line / pulse) | | active | boolean | true | Whether the animation is playing | | borderRadius | number | auto-detected | Custom border radius in px | | brightness | number | per-type (1.3) | Glow brightness multiplier | | saturation | number | 1.2 | Glow saturation multiplier | | hueRange | number | 30 | Hue rotation range in degrees | | staticColors | boolean | false | Disable hue-shift animation | | class | string | - | Additional class on the wrapper | | style | string | - | Additional inline styles on the wrapper | | onActivate | () => void | - | Called when fade-in completes | | onDeactivate | () => void | - | Called when fade-out completes |

All standard HTMLDivElement attributes (id, role, aria-*, data-*, DOM event handlers, ...) are also forwarded to the wrapper.

How it works

BorderBeam renders a wrapper <div> with:

• ::after - the beam stroke (rotate: conic gradient masked to the border; pulse: the colored perimeter ring / hairline)
• ::before - inner glow layer (pulse-outside pushes this outward behind the content)
• [data-beam-bloom] - outer bloom/glow child div

All effect layers are absolutely positioned and use pointer-events: none, so they never interfere with your content. The rotate and line types animate via CSS @property keyframes for smooth GPU-accelerated transitions. The pulse types drive their slow breathing from a single shared, frame-rate-capped (~30fps) requestAnimationFrame loop that writes plain CSS custom properties - so the breathing works even without @property support, repaints less often, and automatically pauses when the instance is inactive, offscreen, or the user prefers reduced motion.

Each instance injects a small, [data-beam="…"]-scoped <style> element containing its generated CSS, so multiple beams with different settings coexist without conflict.

Project structure

svelte-border-beam/
├── src/
│   ├── lib/
│   │   ├── index.ts          # Public exports
│   │   ├── BorderBeam.svelte  # Svelte 5 component (new)
│   │   ├── types.ts           # Type definitions (retyped for Svelte)
│   │   ├── styles.ts          # CSS generation engine (from original, logic unchanged)
│   │   └── pulseDriver.ts     # Shared rAF loop (from original, logic unchanged)
│   └── routes/                # SvelteKit demo site
├── LICENSE
├── CREDITS.md
└── README.md

Requirements

• Svelte 5+
• Modern browser with CSS @property support (Chrome 85+, Safari 15.4+, Firefox 128+)

Accessibility

The effect layers are purely decorative and use pointer-events: none. They do not affect keyboard navigation or screen readers. The pulse types ship a built-in prefers-reduced-motion: reduce block that disables their animations.

Development

npm install
npm run dev        # run the demo site
npm run build      # build the demo + package the library
npm run check      # type-check

Credits

Original border-beam React component, effect design, and all visual tuning by Jakub Antalik, github.com/Jakubantalik/border-beam. See CREDITS.md for details.

License

MIT - same as the original project.