Hi there,
Modify the menu hover underline CSS to this:
@media (min-width: 835px) {
.main-navigation .menu > .menu-item:not(.nav-button) > a::after {
content: "";
position: absolute;
right: 0;
left: 50%;
bottom: 12px;
-webkit-transform: translate3d(-50%,0,0);
transform: translate3d(-50%,0,0);
display: block;
width: 0;
height: 1.5px;
background-color: currentColor;
transition: 0.2s width ease;
}
.main-navigation .menu > .menu-item.current-menu-item:not(.nav-button) > a::after,
.main-navigation .menu > .menu-item.current-menu-ancestor:not(.nav-button) > a::after,
.main-navigation .menu > .menu-item:not(.nav-button) > a:hover::after {
width: 90%;
}
}