.root {
  position: relative;
  display: inline-block;
  font-weight: 700;
  text-decoration: none;
}

.root::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 100%;
  border-bottom: 2px solid currentColor;
  transform: translateY(1px);
  transition: transform 0.2s;
}

.root.blue {
  color: #2421ab;
}

.root.white {
  color: #fcfcfc;
}

.root.regular {
  font-size: 16px;
  line-height: 20px;
}

.root.large {
  font-size: 20px;
  line-height: 28px;
}

@media (min-width: 768px) {
  .root::after {
    border-bottom: 3px solid currentColor;
  }

  .root:hover::after {
    transform: translateY(2px);
    transition: transform 0.2s;
  }

  .root.regular {
    font-size: 20px;
    line-height: 28px;
  }

  .root.large {
    font-size: 28px;
    line-height: 40px;
  }
}

.root {
  position: relative;
  display: inline-block;
  font-weight: 700;
  text-decoration: none;
}

.root::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 100%;
  border-bottom: 2px solid currentColor;
  transform: translateY(1px);
  transition: transform 0.2s;
}

.root.blue {
  color: #2421ab;
}

.root.white {
  color: #fcfcfc;
}

.root.regular {
  font-size: 16px;
  line-height: 20px;
}

.root.large {
  font-size: 20px;
  line-height: 28px;
}

@media (min-width: 768px) {
  .root:hover::after {
    transform: translateY(2px);
    transition: transform 0.2s;
  }

  .root.regular {
    font-size: 20px;
    line-height: 28px;
  }

  .root.large {
    font-size: 28px;
    line-height: 40px;
  }
}

Change CTA underline weight on desktop
Change CTA underline weight on desktop
