Pulsing Gradient Border: CSS Border Animation

Pulsing Gradient Border

A gradient ring swells outward and thins again like slow breathing while its colors turn. The width is a registered @property length on a masked layer, so the box itself never changes size.

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

Pulsing border

Color Base size 16px Dark background Hold hover state

HTML

<div class="bdr-pulsing-gradient-border">Pulsing border</div>

CSS

@property --bdr-pulsing-gradient-border-w {
  syntax: "<length>";
  inherits: false;
  initial-value: 0px;
}
@property --bdr-pulsing-gradient-border-a {
  syntax: "<angle>";
  inherits: false;
  initial-value: 0deg;
}
.bdr-pulsing-gradient-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) 10%, #0b0f19);
  color: #f1f5f9;
}
.bdr-pulsing-gradient-border::before {
  content: "";
  position: absolute;
  inset: calc(var(--bdr-pulsing-gradient-border-w) * -1);
  padding: var(--bdr-pulsing-gradient-border-w);
  border-radius: calc(1em + var(--bdr-pulsing-gradient-border-w));
  background: conic-gradient(from var(--bdr-pulsing-gradient-border-a), var(--c), color-mix(in oklch, var(--c), #ec4899 75%), color-mix(in oklch, var(--c), #8b5cf6 60%), var(--c));
  -webkit-mask: linear-gradient(#000 0 0) content-box, linear-gradient(#000 0 0);
  -webkit-mask-composite: xor;
  mask: linear-gradient(#000 0 0) content-box exclude, linear-gradient(#000 0 0);
  pointer-events: none;
  animation:
    bdr-pulsing-gradient-border-breathe 2.4s cubic-bezier(0.45, 0, 0.55, 1) infinite,
    bdr-pulsing-gradient-border-turn 9.6s linear infinite;
}
@keyframes bdr-pulsing-gradient-border-breathe {
  0%, 100% { --bdr-pulsing-gradient-border-w: 0.1em; opacity: 0.7; }
  50%      { --bdr-pulsing-gradient-border-w: 0.45em; opacity: 1; }
}
@keyframes bdr-pulsing-gradient-border-turn {
  to { --bdr-pulsing-gradient-border-a: 360deg; }
}

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

HTML

CSS

Customizing this snippet

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