Answers for "css hover underline animation"

text underline hover css

a:hover {
  text-decoration: underline;
}

underline css animation hover

.hover-underline-animation {
  display: inline-block;
  position: relative;
  color: #0087ca;
}

.hover-underline-animation:after {
  content: '';
  position: absolute;
  width: 100%;
  transform: scaleX(0);
  height: 2px;
  bottom: 0;
  left: 0;
  background-color: #0087ca;
  transform-origin: bottom right;
  transition: transform 0.25s ease-out;
}

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

add expanding underline on page load css

#sec {
  display: inline-block;
  position: relative;
  padding-bottom: 3px;
}
#sec:after {
  content: '';
  display: block;
  margin: auto;
  height: 3px;
  width: 0px;
  background: transparent;
  transition: width .5s ease, background-color .5s ease;
}
#sec:hover:after {
  width: 100%;
  background: blue;
}