.wp-block-navigation-item__content {
  position: relative;
}

a {
  position: relative;
  display: inline-block;
  z-index: 1;
}

.nav-underline-box {
  position: absolute;
  left: 0;
  bottom: -6px;
  width: 100%;
  height: 20px;
  pointer-events: none;
}

.nav-underline-box svg {
  position: absolute;
  top: 10px;
  z-index: 0;
  width: 100%;
  height: 100%;
  display: block;
}