Blinking Border
A warning border that flashes twice, holds, and repeats, so the box grabs attention without moving. The flash is a hard step on the border layer's opacity, not a fade, like an alarm light.
Also known as: css border blink animation, css border flash animation, flashing border css.
Unsaved changes
HTML
<div class="bdr-blinking-border"> <svg class="bdr-blinking-border-icon" viewBox="0 0 24 24" aria-hidden="true"><path d="M12 3 2 20h20L12 3Z"/><path d="M12 10v4m0 3v.01"/></svg> Unsaved changes </div>
CSS
.bdr-blinking-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;
grid-auto-flow: column;
gap: 0.5em;
justify-content: center;
background: color-mix(in srgb, var(--c) 7%, transparent);
}
.bdr-blinking-border::before {
content: "";
position: absolute;
inset: 0;
border: 0.14em solid var(--c);
border-radius: inherit;
box-shadow: 0 0 0.7em color-mix(in srgb, var(--c) 55%, transparent), inset 0 0 0.5em color-mix(in srgb, var(--c) 30%, transparent);
pointer-events: none;
animation: bdr-blinking-border-flash 2.2s step-end infinite;
}
.bdr-blinking-border-icon {
width: 1.3em;
height: 1.3em;
fill: none;
stroke: var(--c);
stroke-width: 2;
stroke-linecap: round;
stroke-linejoin: round;
}
@keyframes bdr-blinking-border-flash {
0%, 20%, 100% { opacity: 1; }
10%, 30% { opacity: 0.12; }
40% { opacity: 1; }
}
@media (prefers-reduced-motion: reduce) {
.bdr-blinking-border, .bdr-blinking-border *, .bdr-blinking-border::before, .bdr-blinking-border::after, .bdr-blinking-border *::before, .bdr-blinking-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.