Radial Glow Fill Button
A soft-edged radial fill blooms up from below the button and leaves a lighter glow at the bottom center. The radius is a registered @property, so the feathered edge travels smoothly.
Also known as: radial gradient fill hover, soft radial fill, glow from below button.
HTML
<button class="hfx-radial-glow-fill">Go live</button>
CSS
@property --hfx-radial-glow-fill-r {
syntax: "<percentage>";
inherits: false;
initial-value: 0%;
}
.hfx-radial-glow-fill {
--c: var(--hfx-color, #3b82f6);
position: relative;
isolation: isolate;
overflow: hidden;
display: inline-flex;
align-items: center;
justify-content: center;
gap: 0.5em;
padding: 0.75em 1.75em;
border-radius: 0.5em;
font: 600 var(--hfx-size, 16px)/1.2 system-ui, sans-serif;
white-space: nowrap;
cursor: pointer;
border: 2px solid var(--c);
background: transparent;
color: var(--c);
transition: color 0.25s ease 0.2s;
}
.hfx-radial-glow-fill::before {
content: "";
position: absolute;
inset: 0;
z-index: -1;
background: radial-gradient(
circle at 50% 130%,
color-mix(in srgb, var(--c) 45%, #fff) 0,
var(--c) calc(var(--hfx-radial-glow-fill-r) * 0.5),
var(--c) calc(var(--hfx-radial-glow-fill-r) * 0.75),
transparent var(--hfx-radial-glow-fill-r)
);
transition: --hfx-radial-glow-fill-r 0.6s cubic-bezier(0.4, 0, 0.2, 1);
}
.hfx-radial-glow-fill:is(:hover, :focus-visible) {
background-color: var(--c); /* hides the hairline where the fill meets the border */
color: #fff;
transition: color 0.25s ease 0.2s, background-color 0s 0.6s;
}
.hfx-radial-glow-fill:is(:hover, :focus-visible)::before { --hfx-radial-glow-fill-r: 150%; }
@media (prefers-reduced-motion: reduce) {
.hfx-radial-glow-fill, .hfx-radial-glow-fill *, .hfx-radial-glow-fill::before, .hfx-radial-glow-fill::after, .hfx-radial-glow-fill *::before, .hfx-radial-glow-fill *::after {
animation-duration: 0.01ms !important;
animation-iteration-count: 1 !important;
transition-duration: 0.01ms !important;
}
}Customizing this snippet
- Color: set
--hfx-coloron the element or a parent. Currently previewing#3b82f6. - Base size: set
--hfx-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.