Electric Border: CSS Border Animation

Electric Border

A crackling line of electricity wraps a dark panel and jumps between three shapes like an arc. SVG turbulence displaces each copy of the outline, and a stepped opacity loop flips between them.

Also known as: lightning border css, electric border animation, crackling energy border.

High voltage

Color Base size 16px Dark background Hold hover state

HTML

<div class="bdr-electric-border">
  <svg class="bdr-electric-border-svg" viewBox="0 0 150 85" preserveAspectRatio="none" aria-hidden="true">
    <defs>
      <filter id="bdr-electric-border-a" x="-10%" y="-15%" width="120%" height="130%"><feTurbulence type="turbulence" baseFrequency="0.06" numOctaves="2" seed="2"/><feDisplacementMap in="SourceGraphic" scale="5"/></filter>
      <filter id="bdr-electric-border-b" x="-10%" y="-15%" width="120%" height="130%"><feTurbulence type="turbulence" baseFrequency="0.06" numOctaves="2" seed="7"/><feDisplacementMap in="SourceGraphic" scale="5"/></filter>
      <filter id="bdr-electric-border-c" x="-10%" y="-15%" width="120%" height="130%"><feTurbulence type="turbulence" baseFrequency="0.06" numOctaves="2" seed="13"/><feDisplacementMap in="SourceGraphic" scale="5"/></filter>
    </defs>
    <rect class="bdr-electric-border-halo" x="3" y="3" width="144" height="79" rx="9"/>
    <rect class="bdr-electric-border-arc" x="3" y="3" width="144" height="79" rx="9" filter="url(#bdr-electric-border-a)"/>
    <rect class="bdr-electric-border-arc" x="3" y="3" width="144" height="79" rx="9" filter="url(#bdr-electric-border-b)"/>
    <rect class="bdr-electric-border-arc" x="3" y="3" width="144" height="79" rx="9" filter="url(#bdr-electric-border-c)"/>
  </svg>
  <span class="bdr-electric-border-text">High voltage</span>
</div>

CSS

.bdr-electric-border {
  --c: var(--bdr-color, #3b82f6);
  font-size: var(--bdr-size, 16px);
  position: relative;
  display: grid;
  place-items: center;
  width: 15em;
  height: 8.5em;
  border-radius: 1em;
  font-family: system-ui, sans-serif;
  font-weight: 600;
  background: color-mix(in srgb, var(--c) 8%, #07070c);
  color: color-mix(in srgb, var(--c) 30%, #fff);
}
.bdr-electric-border-svg {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  overflow: visible;
  filter: drop-shadow(0 0 0.2em var(--c)) drop-shadow(0 0 0.5em color-mix(in srgb, var(--c) 70%, transparent));
  pointer-events: none;
}
.bdr-electric-border-svg rect { fill: none; }
.bdr-electric-border-halo {
  stroke: color-mix(in srgb, var(--c) 30%, transparent);
  stroke-width: 2.5;
}
.bdr-electric-border-arc {
  stroke: color-mix(in srgb, var(--c) 45%, #fff);
  stroke-width: 1.2;
  opacity: 0;
  animation: bdr-electric-border-zap 0.36s step-end infinite;
}
.bdr-electric-border-arc:nth-of-type(3) { animation-delay: -0.12s; }
.bdr-electric-border-arc:nth-of-type(4) { animation-delay: -0.24s; }
.bdr-electric-border-text {
  position: relative;
  letter-spacing: 0.04em;
  text-shadow: 0 0 0.4em var(--c);
}
@keyframes bdr-electric-border-zap {
  0%        { opacity: 1; }
  33.3%, 100% { opacity: 0; }
}

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

Customizing this snippet

Color: set --bdr-color on the element or a parent. Currently previewing #3b82f6.
Base size: set --bdr-size. Every other dimension is in em, so the whole thing scales together. Currently previewing 16px.
Speed: change the duration on the transition or animation shorthand. Staggered delays are relative, so they keep their rhythm.
Reduced motion: the rule at the end of the CSS turns the motion off for people who asked their OS for less of it. Keep it.

Electric Border

HTML

CSS

Customizing this snippet

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