Loading Border: CSS Border Animation

Loading Border

An arc chases itself around the box, stretching out and snapping short like the Material spinner, for boxes that are busy but have no progress to show. Dash length and offset share one keyframe.

Also known as: css border loading animation, border spinner css, indeterminate border progress.

Uploading

Color Base size 16px Dark background Hold hover state

HTML

<div class="bdr-loading-border">
  <svg class="bdr-loading-border-svg" aria-hidden="true">
    <rect class="bdr-loading-border-track" width="100%" height="100%"/>
    <rect class="bdr-loading-border-arc" width="100%" height="100%" pathLength="100"/>
  </svg>
  Uploading
</div>

CSS

.bdr-loading-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) 5%, transparent);
}
.bdr-loading-border-svg {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  overflow: visible;
  pointer-events: none;
}
.bdr-loading-border-svg rect {
  rx: 1em;
  fill: none;
  stroke-width: 0.16em;
}
.bdr-loading-border-track { stroke: color-mix(in srgb, var(--c) 15%, transparent); }
.bdr-loading-border-arc {
  stroke: var(--c);
  stroke-linecap: round;
  animation: bdr-loading-border-chase 1.8s cubic-bezier(0.4, 0, 0.2, 1) infinite;
}
@keyframes bdr-loading-border-chase {
  0%   { stroke-dasharray: 1 99; stroke-dashoffset: 0; }
  50%  { stroke-dasharray: 42 58; stroke-dashoffset: -8; }
  100% { stroke-dasharray: 1 99; stroke-dashoffset: -99; }
}

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

Loading Border

HTML

CSS

Customizing this snippet

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