Glowing Underline Animation
A glowing comet runs along a faint underline and trails off, over and over, for launch and coming soon lines. The comet is a gradient tile on a pseudo-element with a drop-shadow glow.
Also known as: comet underline css, light running along underline, animated underline glow.
Coming soon
HTML
<div class="txt-glowing-underline-text">Coming soon</div>
CSS
.txt-glowing-underline-text {
--c: var(--txt-color, #3b82f6);
font-size: var(--txt-size, 32px);
font-family: system-ui, sans-serif;
font-weight: 700;
line-height: 1.2;
position: relative;
display: inline-block;
padding-bottom: 0.28em;
white-space: nowrap;}
.txt-glowing-underline-text::before,
.txt-glowing-underline-text::after {
content: "";
position: absolute;
left: 0;
right: 0;
border-radius: 1em;
}
.txt-glowing-underline-text::before {
bottom: 0.06em;
height: 0.05em;
background: color-mix(in srgb, var(--c) 25%, transparent);
}
.txt-glowing-underline-text::after {
bottom: 0.04em;
height: 0.09em;
background: linear-gradient(90deg, transparent, var(--c) 85%, color-mix(in srgb, var(--c) 35%, #fff)) no-repeat;
background-size: 40% 100%;
filter: drop-shadow(0 0 0.12em var(--c));
animation: txt-glowing-underline-text-run 2.2s cubic-bezier(0.45, 0, 0.55, 1) infinite;
}
/* -70% and 170% park the 40% tile just outside each end */
@keyframes txt-glowing-underline-text-run {
from { background-position: -70% 0; }
to { background-position: 170% 0; }
}
@media (prefers-reduced-motion: reduce) {
.txt-glowing-underline-text, .txt-glowing-underline-text *, .txt-glowing-underline-text::before, .txt-glowing-underline-text::after, .txt-glowing-underline-text *::before, .txt-glowing-underline-text *::after {
animation-duration: 0.01ms !important;
animation-iteration-count: 1 !important;
transition-duration: 0.01ms !important;
}
}Customizing this snippet
- Color: set
--txt-coloron the element or a parent. Currently previewing#3b82f6. - Font size: set
--txt-size. Every other dimension is inem, so the whole thing scales together. Currently previewing40px. - 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.