Marching Ants Border
The two-tone dashed outline of a selection box, marching clockwise with resize handles on every corner and edge. The dashes live on an SVG rect with pathLength, so the loop has no seam.
Also known as: animated dashed border css, css border dashed animation, selection box border.
Selection
HTML
<div class="bdr-marching-ants-border">
<svg class="bdr-marching-ants-border-svg" aria-hidden="true">
<rect class="bdr-marching-ants-border-base" width="100%" height="100%"/>
<rect class="bdr-marching-ants-border-ants" width="100%" height="100%" pathLength="100"/>
</svg>
Selection
</div>CSS
.bdr-marching-ants-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;
border-radius: 0;
background: color-mix(in srgb, var(--c) 7%, transparent);
}
.bdr-marching-ants-border-svg {
position: absolute;
inset: 0;
width: 100%;
height: 100%;
overflow: visible;
pointer-events: none;
}
.bdr-marching-ants-border-svg rect {
fill: none;
stroke-width: 0.1em;
}
.bdr-marching-ants-border-base { stroke: color-mix(in srgb, var(--c) 12%, #fff); }
.bdr-marching-ants-border-ants {
stroke: var(--c);
stroke-dasharray: 1 1;
animation: bdr-marching-ants-border-march 0.9s linear infinite;
}
.bdr-marching-ants-border::after {
content: "";
position: absolute;
inset: -0.25em;
--h: linear-gradient(var(--c) 0 0);
background:
var(--h) 0 0, var(--h) 50% 0, var(--h) 100% 0,
var(--h) 0 50%, var(--h) 100% 50%,
var(--h) 0 100%, var(--h) 50% 100%, var(--h) 100% 100%;
background-size: 0.5em 0.5em;
background-repeat: no-repeat;
pointer-events: none;
}
@keyframes bdr-marching-ants-border-march {
to { stroke-dashoffset: -2; }
}
@media (prefers-reduced-motion: reduce) {
.bdr-marching-ants-border, .bdr-marching-ants-border *, .bdr-marching-ants-border::before, .bdr-marching-ants-border::after, .bdr-marching-ants-border *::before, .bdr-marching-ants-border *::after {
animation-duration: 0.01ms !important;
animation-iteration-count: 1 !important;
transition-duration: 0.01ms !important;
}
}Customizing this snippet
- Color: set
--bdr-coloron the element or a parent. Currently previewing#3b82f6. - Base size: set
--bdr-size. Every other dimension is inem, so the whole thing scales together. Currently previewing16px. - Speed: change the duration on the
transitionoranimationshorthand. 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.