animation

CSS Animated Underline on Hover

Sliding underline effect on links and nav items using CSS transform and pseudo-elements.

An animated underline on hover creates polish without being distracting. The technique uses a ::after pseudo-element as the underline, scaled to zero by default. On hover, it scales to full width. By toggling transform-origin between 'right' and 'left', the underline slides in from the left and exits to the right — a subtle directional detail that feels intentional.

Live CSS Editor

CSS

Preview

/* Slide-in underline */
.underline-link {
  position: relative;
  text-decoration: none;
  color: inherit;
}

.underline-link::after {
  content: "";
  position: absolute;
  bottom: -2px;
  left: 0;
  width: 100%;
  height: 2px;
  background: currentColor;
  transform: scaleX(0);
  transform-origin: right;
  transition: transform 0.3s ease;
}

.underline-link:hover::after {
  transform: scaleX(1);
  transform-origin: left;
}

/* Accent color underline */
.underline-accent::after {
  background: #1d9e75;
}

/* Thick underline variant */
.underline-thick::after {
  height: 3px;
  bottom: -3px;
  border-radius: 2px;
}

/* Center-out underline */
.underline-center::after {
  transform-origin: center;
}

.underline-center:hover::after {
  transform: scaleX(1);
  transform-origin: center;
}

/* Fill underline (background-size technique) */
.underline-fill {
  background-image: linear-gradient(#1d9e75, #1d9e75);
  background-position: 0% 100%;
  background-repeat: no-repeat;
  background-size: 0% 2px;
  transition: background-size 0.3s ease;
  text-decoration: none;
}

.underline-fill:hover {
  background-size: 100% 2px;
}

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Usage Note

Put the transition on the ::after default state, not the :hover state — this ensures both entry and exit animate. The transform-origin swap (right → left) makes the underline slide in from the left on hover and retract to the right on mouse-leave.