Flash Update Border: CSS Border Animation

Flash Update Border

A balance card whose border flashes bright and decays each time the number ticks over, the way trading and finance dashboards flag a live update. One keyframe snaps the flash on and eases it out.

Also known as: flash border, flash border animation css, highlight on update css, value changed flash.

Total balance $12,480.20$12,806.45 +2.6% today

Color Base size 16px Dark background Hold hover state

HTML

<div class="bdr-flash-update-border">
  <span class="bdr-flash-update-border-label">Total balance</span>
  <span class="bdr-flash-update-border-value"><span>$12,480.20</span><span>$12,806.45</span></span>
  <span class="bdr-flash-update-border-delta">+2.6% today</span>
</div>

CSS

.bdr-flash-update-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;
  box-sizing: border-box;
  place-items: initial;
  align-content: center;
  gap: 0.3em;
  padding: 0 1.4em;
  background: color-mix(in srgb, var(--c) 5%, transparent);
  box-shadow: inset 0 0 0 1px color-mix(in srgb, var(--c) 20%, transparent);
}
.bdr-flash-update-border::after {
  content: "";
  position: absolute;
  inset: 0;
  border-radius: inherit;
  background: color-mix(in srgb, var(--c) 10%, transparent);
  box-shadow:
    inset 0 0 0 0.12em color-mix(in srgb, var(--c) 70%, #fff),
    0 0 0 0.12em color-mix(in srgb, var(--c) 30%, transparent),
    0 0 1.6em color-mix(in srgb, var(--c) 45%, transparent);
  opacity: 0;
  pointer-events: none;
  animation: bdr-flash-update-border-flash 3s infinite;
}
.bdr-flash-update-border-label {
  font-size: 0.72em;
  font-weight: 500;
  opacity: 0.6;
}
.bdr-flash-update-border-value {
  display: grid;
  overflow: hidden;
  font-size: 1.6em;
  font-weight: 650;
  letter-spacing: -0.02em;
  font-variant-numeric: tabular-nums;
}
.bdr-flash-update-border-value span {
  grid-area: 1 / 1;
  animation: bdr-flash-update-border-tick 6s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}
.bdr-flash-update-border-value span + span { animation-delay: -3s; }
.bdr-flash-update-border-delta {
  justify-self: start;
  padding: 0.2em 0.5em;
  border-radius: 1em;
  background: color-mix(in srgb, var(--c) 14%, transparent);
  color: var(--c);
  font-size: 0.7em;
}
@keyframes bdr-flash-update-border-flash {
  0%   { opacity: 0; animation-timing-function: cubic-bezier(0.2, 0, 0.4, 1); }
  3%   { opacity: 1; animation-timing-function: cubic-bezier(0.1, 0.6, 0.3, 1); }
  45%, 100% { opacity: 0; }
}
@keyframes bdr-flash-update-border-tick {
  0%        { opacity: 0; transform: translateY(0.5em); }
  5%, 50%   { opacity: 1; transform: none; }
  54%, 100% { opacity: 0; transform: translateY(-0.5em); }
}
@media (prefers-reduced-motion: reduce) {
  .bdr-flash-update-border::after { animation: none; }
  .bdr-flash-update-border-value span { animation: none; }
  .bdr-flash-update-border-value span + span { opacity: 0; }
}

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

Flash Update Border

HTML

CSS

Customizing this snippet

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