Morphing Underline Animation
The underline gathers into a dot, hops over the word and lands as its full stop, then drops and rolls back to stretch out again. One pseudo-element: clip-path trims it, transform moves it.
Also known as: underline to dot animation, bouncing dot underline css, playful underline loop.
Say hello
HTML
<div class="txt-morphing-underline">Say <span class="txt-morphing-underline-word">hello</span></div>
CSS
.txt-morphing-underline {
--c: var(--txt-color, #3b82f6);
font-size: var(--txt-size, 32px);
font-family: system-ui, sans-serif;
font-weight: 700;
line-height: 1.2;
padding: 0.6em 0.4em 0.2em 0;
white-space: nowrap;}
.txt-morphing-underline-word {
position: relative;
display: inline-block;
color: var(--c);
}
.txt-morphing-underline-word::after {
content: "";
position: absolute;
left: 0;
right: 0;
bottom: -0.1em;
height: 0.1em;
background: var(--c);
clip-path: inset(0 0 round 0.05em);
transform-origin: 50% 100%;
animation: txt-morphing-underline-hop 4s cubic-bezier(0.65, 0, 0.35, 1) infinite;
}
/*
* calc(50% - 0.05em) trims the full-width bar to a 0.1em dot at its center.
* The hop is five points on a parabola; translateX percentages are of the
* bar, which is the word's width, so 50% + 0.1em lands just past the last letter.
*/
@keyframes txt-morphing-underline-hop {
0%, 10% { clip-path: inset(0 0 round 0.05em); transform: none; }
22% { clip-path: inset(0 calc(50% - 0.05em) round 0.05em); transform: none; }
24% { transform: scale(1.3, 0.7); animation-timing-function: linear; }
28% { transform: translate(calc(12.5% + 0.025em), -1.18em); animation-timing-function: linear; }
32% { transform: translate(calc(25% + 0.05em), -1.62em); animation-timing-function: linear; }
36% { transform: translate(calc(37.5% + 0.075em), -1.35em); animation-timing-function: linear; }
40% { transform: translate(calc(50% + 0.1em), -0.35em) scale(1.8, 1); animation-timing-function: ease-out; }
46%, 72% { transform: translate(calc(50% + 0.1em), -0.35em) scale(1.4); }
78% { transform: translate(calc(50% + 0.1em), 0); animation-timing-function: ease-in-out; }
84% { clip-path: inset(0 calc(50% - 0.05em) round 0.05em); transform: none; }
94%, 100% { clip-path: inset(0 0 round 0.05em); transform: none; }
}
@media (prefers-reduced-motion: reduce) {
.txt-morphing-underline, .txt-morphing-underline *, .txt-morphing-underline::before, .txt-morphing-underline::after, .txt-morphing-underline *::before, .txt-morphing-underline *::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.