Fire Border
Flame colors climb both sides of a dark box while a hot, flickering glow leaks out and upward. A vertical gradient loops its position upward, and a blurred copy flickers in opacity behind it.
Also known as: fire border animation css, flame border css, burning border effect.
On fire
HTML
<div class="bdr-fire-border">On fire</div>
CSS
.bdr-fire-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;
--ember: color-mix(in srgb, var(--c) 8%, #140806);
--fire: linear-gradient(0deg, #7f1d1d, #dc2626, #f97316, #fbbf24, #fef3c7, #fbbf24, #f97316, #dc2626, #7f1d1d) 0 0 / 100% 5em;
isolation: isolate;
color: #fde68a;
letter-spacing: 0.04em;
}
.bdr-fire-border::before,
.bdr-fire-border::after {
content: "";
position: absolute;
z-index: -1;
border-radius: inherit;
pointer-events: none;
}
.bdr-fire-border::before {
inset: 0.1em 0.15em 0.5em;
background: var(--fire);
filter: blur(0.55em);
transform: translateY(-0.2em);
animation:
bdr-fire-border-rise 1.6s linear infinite,
bdr-fire-border-flicker 1.9s linear infinite;
}
.bdr-fire-border::after {
inset: 0;
border: 0.18em solid transparent;
background: linear-gradient(var(--ember), var(--ember)) padding-box, var(--fire) border-box;
animation: bdr-fire-border-rise 1.6s linear infinite;
}
@keyframes bdr-fire-border-rise {
to { background-position: 0 -5em; }
}
@keyframes bdr-fire-border-flicker {
0%, 100% { opacity: 0.8; }
12% { opacity: 0.55; }
27% { opacity: 0.95; }
41% { opacity: 0.6; }
58% { opacity: 1; }
73% { opacity: 0.65; }
88% { opacity: 0.9; }
}
@media (prefers-reduced-motion: reduce) {
.bdr-fire-border, .bdr-fire-border *, .bdr-fire-border::before, .bdr-fire-border::after, .bdr-fire-border *::before, .bdr-fire-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.