Corner Brackets Border
Four corner brackets stretch along the edges until they close into a full frame, hold, then pull back into corners. Eight gradient strips on one pseudo-element, sized by a single keyframe.
Also known as: css animated corners, corner border animation, corners to full border.
In focus
HTML
<div class="bdr-corner-brackets-border">In focus</div>
CSS
.bdr-corner-brackets-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: 0.2em;
background: color-mix(in srgb, var(--c) 6%, transparent);
}
.bdr-corner-brackets-border::before {
content: "";
position: absolute;
inset: 0;
--h: linear-gradient(var(--c) 0 0) no-repeat;
background:
var(--h) 0 0, var(--h) 0 0,
var(--h) 100% 0, var(--h) 100% 0,
var(--h) 0 100%, var(--h) 0 100%,
var(--h) 100% 100%, var(--h) 100% 100%;
pointer-events: none;
animation: bdr-corner-brackets-border-close 4s cubic-bezier(0.7, 0, 0.3, 1) infinite;
}
@keyframes bdr-corner-brackets-border-close {
0%, 12%, 100% { background-size: 1.4em 0.16em, 0.16em 1.4em; }
44%, 68% { background-size: 51% 0.16em, 0.16em 51%; }
}
@media (prefers-reduced-motion: reduce) {
.bdr-corner-brackets-border, .bdr-corner-brackets-border *, .bdr-corner-brackets-border::before, .bdr-corner-brackets-border::after, .bdr-corner-brackets-border *::before, .bdr-corner-brackets-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.