.wp-block-navigation .menu-item-has-children > .sub-menu {
  display: flex;
  flex-direction: row;
  gap: 20px;
  padding: 10px 0;
  min-width: 250px;
  width: auto;
}

.wp-block-navigation .menu-item-has-children > .sub-menu li {
  list-style: none;
  display: inline-block;
  padding: 5px 10px;
}

.wp-block-navigation .menu-item-has-children > .sub-menu {
  background-color: #fff; 
  border: 1px solid #ddd;
}