body {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background: #f8f8f8;
  font: normal 400 130%/1.5 -apple-system, BlinkMacSystemFont, Helvetica, Arial, sans-serif;
}

nav {
  display: grid;
  grid-auto-flow: column;
  grid-gap: 1em;
}

a {
  position: relative;
  font-weight: 600;
  text-decoration: none;
  color: rgba(0, 0, 0, 0.4);
  transition: color .3s ease;
}
a::after {
  --scale: 0;
  content: '';
  position: absolute;
  left: 0;
  right: 0;
  top: 100%;
  height: 3px;
  background: #4c81c9;
  -webkit-transform: scaleX(var(--scale));
          transform: scaleX(var(--scale));
  -webkit-transform-origin: var(--x) 50%;
          transform-origin: var(--x) 50%;
  transition: -webkit-transform 0.3s cubic-bezier(0.535, 0.05, 0.355, 1);
  transition: transform 0.3s cubic-bezier(0.535, 0.05, 0.355, 1);
  transition: transform 0.3s cubic-bezier(0.535, 0.05, 0.355, 1), -webkit-transform 0.3s cubic-bezier(0.535, 0.05, 0.355, 1);
}
a:hover {
  color: #4c81c9;
}
a:hover::after {
  --scale: 1;
}