.wp-block-navigation .wp-block-navigation-item .wp-block-navigation-item__content[aria-current="page"] {
    position: relative;
}

.wp-block-navigation .wp-block-navigation-item .wp-block-navigation-item__content[aria-current="page"]::after {
    content: "";
    position: absolute;
    background-color: var(--wp--preset--color--primary);
    border-radius: 100em;
    height: 3px;
    width: 100%;
    left: 0;
    bottom: -3px;
}