Pulsing Glow Border: CSS Border Animation

Pulsing Glow Border

The border and its glow beat twice, then rest, like a heartbeat monitor. Good for live, recording or needs-attention states. A shadow ring on a pseudo-element scales and fades on a lub-dub keyframe.

Also known as: pulsating glow effect css, heartbeat glow border, glow pulse animation.

Recording

Color Base size 16px Dark background Hold hover state

HTML

<div class="bdr-pulsing-glow-border"><span class="bdr-pulsing-glow-border-dot"></span>Recording</div>

CSS

.bdr-pulsing-glow-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;
  --beat: 1.4s cubic-bezier(0.33, 0, 0.2, 1) infinite;
  grid-auto-flow: column;
  gap: 0.5em;
  justify-content: center;
  border: 0.12em solid var(--c);
  box-sizing: border-box;
  background: color-mix(in srgb, var(--c) 6%, transparent);
}
.bdr-pulsing-glow-border::before {
  content: "";
  position: absolute;
  inset: -0.12em;
  border-radius: inherit;
  box-shadow: 0 0 0.3em 0.1em var(--c), 0 0 1.4em color-mix(in srgb, var(--c) 60%, transparent), inset 0 0 0.9em color-mix(in srgb, var(--c) 35%, transparent);
  pointer-events: none;
  animation: bdr-pulsing-glow-border-beat var(--beat);
}
.bdr-pulsing-glow-border-dot {
  width: 0.6em;
  height: 0.6em;
  border-radius: 50%;
  background: var(--c);
  box-shadow: 0 0 0.5em var(--c);
  animation: bdr-pulsing-glow-border-beat var(--beat);
}
@keyframes bdr-pulsing-glow-border-beat {
  0%, 100% { opacity: 0.25; transform: scale(1); }
  10%      { opacity: 1; transform: scale(1.025); }
  20%      { opacity: 0.45; transform: scale(1); }
  32%      { opacity: 0.95; transform: scale(1.02); }
  60%      { opacity: 0.25; transform: scale(1); }
}

@media (prefers-reduced-motion: reduce) {
  .bdr-pulsing-glow-border, .bdr-pulsing-glow-border *, .bdr-pulsing-glow-border::before, .bdr-pulsing-glow-border::after, .bdr-pulsing-glow-border *::before, .bdr-pulsing-glow-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.

Pulsing Glow Border

HTML

CSS

Customizing this snippet

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