Glowing Progress Bar
A thin bar that fills in uneven bursts behind a bright glowing head, which flares when it reaches the end. The head is one element with a static glow that only moves by transform.
Also known as: neon progress bar, progress bar with glow, comet loading bar.
HTML
<div class="ldr-glowing-progress-bar" role="progressbar" aria-label="Loading"><span></span></div>
CSS
.ldr-glowing-progress-bar {
--s: var(--ldr-size, 48px);
--c: var(--ldr-color, #3b82f6);
--w: calc(var(--s) * 6);
position: relative;
width: var(--w);
height: calc(var(--s) / 12);
border-radius: var(--s);
background: color-mix(in srgb, var(--ldr-color, #3b82f6) 14%, transparent);
}
.ldr-glowing-progress-bar::before {
content: "";
position: absolute;
inset: 0;
border-radius: inherit;
background: linear-gradient(90deg, color-mix(in srgb, var(--ldr-color, #3b82f6) 15%, transparent), var(--c));
box-shadow: 0 0 calc(var(--s) / 6) color-mix(in srgb, var(--ldr-color, #3b82f6) 45%, transparent);
transform-origin: left;
animation: ldr-glowing-progress-bar-fill 3.2s infinite;
}
.ldr-glowing-progress-bar span {
position: absolute;
top: 50%;
left: calc(var(--s) / -8);
width: calc(var(--s) / 4);
height: calc(var(--s) / 4);
margin-top: calc(var(--s) / -8);
border-radius: 50%;
background: radial-gradient(circle, color-mix(in srgb, var(--c) 25%, #fff) 0 30%, var(--c) 70%);
box-shadow: 0 0 calc(var(--s) / 6) calc(var(--s) / 20) var(--c), 0 0 calc(var(--s) / 2) calc(var(--s) / 8) color-mix(in srgb, var(--ldr-color, #3b82f6) 40%, transparent);
animation: ldr-glowing-progress-bar-head 3.2s infinite;
}
@keyframes ldr-glowing-progress-bar-fill {
0% { transform: scaleX(0); animation-timing-function: cubic-bezier(0.3, 0, 0.2, 1); }
20% { transform: scaleX(0.24); animation-timing-function: cubic-bezier(0.5, 0, 0.5, 1); }
32% { transform: scaleX(0.3); animation-timing-function: cubic-bezier(0.4, 0, 0.2, 1); }
54% { transform: scaleX(0.66); animation-timing-function: cubic-bezier(0.5, 0, 0.5, 1); }
64% { transform: scaleX(0.72); animation-timing-function: cubic-bezier(0.5, 0, 0.2, 1); }
82%, 90% { transform: scaleX(1); opacity: 1; }
100% { transform: scaleX(1); opacity: 0; }
}
@keyframes ldr-glowing-progress-bar-head {
0% { transform: translateX(0); animation-timing-function: cubic-bezier(0.3, 0, 0.2, 1); }
20% { transform: translateX(calc(var(--w) * 0.24)); animation-timing-function: cubic-bezier(0.5, 0, 0.5, 1); }
32% { transform: translateX(calc(var(--w) * 0.3)); animation-timing-function: cubic-bezier(0.4, 0, 0.2, 1); }
54% { transform: translateX(calc(var(--w) * 0.66)); animation-timing-function: cubic-bezier(0.5, 0, 0.5, 1); }
64% { transform: translateX(calc(var(--w) * 0.72)); animation-timing-function: cubic-bezier(0.5, 0, 0.2, 1); }
82% { transform: translateX(var(--w)) scale(1); opacity: 1; }
88% { transform: translateX(var(--w)) scale(1.7); opacity: 1; }
100% { transform: translateX(var(--w)) scale(2.4); opacity: 0; }
}
@media (prefers-reduced-motion: reduce) {
.ldr-glowing-progress-bar, .ldr-glowing-progress-bar *, .ldr-glowing-progress-bar::before, .ldr-glowing-progress-bar::after, .ldr-glowing-progress-bar *::before, .ldr-glowing-progress-bar *::after {
animation-duration: 3s;
}
}Customizing this loader
- Color: set
--ldr-coloron the element or a parent. Currently previewing#3b82f6. - Size: set
--ldr-size. Every dimension in the snippet is derived from it. Currently previewing64px. - Speed: change the duration on the
animationshorthand. Delays on the children are relative, so they keep their rhythm. - Accessibility: the root carries
role="status"and anaria-labelso screen readers announce the wait. The reduced-motion rule at the end slows the animation for users who asked for less motion.