Roaming Spotlight Border: CSS Border Animation

Roaming Spotlight Border

A soft spotlight travels the edge of a dark card, lighting the border it touches and washing the surface beside it. Two registered @property percentages walk the light around at one steady speed.

Also known as: spotlight border, spotlight border css, light sweeping border, card spotlight effect.

Preview deployments Every push gets its own URL, live in 41 seconds.

Color Base size 16px Dark background Hold hover state

HTML

<div class="bdr-roaming-spotlight-border">
  <span class="bdr-roaming-spotlight-border-icon" aria-hidden="true"></span>
  <span class="bdr-roaming-spotlight-border-title">Preview deployments</span>
  <span class="bdr-roaming-spotlight-border-text">Every push gets its own URL, live in 41 seconds.</span>
</div>

CSS

@property --bdr-roaming-spotlight-border-x {
  syntax: "<percentage>";
  inherits: true;
  initial-value: 0%;
}
@property --bdr-roaming-spotlight-border-y {
  syntax: "<percentage>";
  inherits: true;
  initial-value: 0%;
}
.bdr-roaming-spotlight-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;
  --at: var(--bdr-roaming-spotlight-border-x) var(--bdr-roaming-spotlight-border-y);
  box-sizing: border-box;
  isolation: isolate;
  place-items: initial;
  align-content: center;
  gap: 0.35em;
  padding: 1.2em 1.3em;
  background: color-mix(in srgb, var(--c) 10%, #0b0f19);
  color: #f1f5f9;
  animation: bdr-roaming-spotlight-border-roam 7s linear infinite;
}
.bdr-roaming-spotlight-border::before,
.bdr-roaming-spotlight-border::after {
  content: "";
  position: absolute;
  inset: 0;
  border-radius: inherit;
  pointer-events: none;
}
.bdr-roaming-spotlight-border::before {
  z-index: -1;
  background: radial-gradient(9em circle at var(--at), color-mix(in srgb, var(--c) 20%, transparent), transparent 70%);
}
.bdr-roaming-spotlight-border::after {
  padding: 2px;
  background:
    radial-gradient(4.5em circle at var(--at), color-mix(in srgb, var(--c) 10%, #fff), var(--c) 35%, transparent 80%),
    color-mix(in srgb, #fff 10%, transparent);
  -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);
}
.bdr-roaming-spotlight-border-icon {
  width: 1.7em;
  height: 1.7em;
  margin-bottom: 0.35em;
  border-radius: 0.45em;
  background:
    linear-gradient(135deg, color-mix(in srgb, var(--c) 30%, #fff), var(--c));
  box-shadow: 0 0.3em 0.8em -0.2em var(--c);
}
.bdr-roaming-spotlight-border-title { font-size: 0.95em; }
.bdr-roaming-spotlight-border-text {
  font-size: 0.75em;
  font-weight: 450;
  line-height: 1.4;
  color: color-mix(in srgb, #f1f5f9 62%, transparent);
}
/* 15em by 8.5em is 47em around, so each side takes its share of the loop. */
@keyframes bdr-roaming-spotlight-border-roam {
  0%, 100% { --bdr-roaming-spotlight-border-x: 0%; --bdr-roaming-spotlight-border-y: 0%; }
  31.9%    { --bdr-roaming-spotlight-border-x: 100%; --bdr-roaming-spotlight-border-y: 0%; }
  50%      { --bdr-roaming-spotlight-border-x: 100%; --bdr-roaming-spotlight-border-y: 100%; }
  81.9%    { --bdr-roaming-spotlight-border-x: 0%; --bdr-roaming-spotlight-border-y: 100%; }
}
@media (prefers-reduced-motion: reduce) {
  .bdr-roaming-spotlight-border {
    animation: none;
    --bdr-roaming-spotlight-border-x: 85%;
    --bdr-roaming-spotlight-border-y: 0%;
  }
}

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

Roaming Spotlight Border

HTML

CSS

Customizing this snippet

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