Suppose you want to add some additional text under Navigation, like this:

You can use this code to Custom CSS box

nav>div.header-nav-item>a:after, div.header-menu-nav-wrapper>div a:after {
    display: block;
    text-align: center;
    font-size: 12px;
}
nav>div.header-nav-item>a {
    text-align: center;
}
/* align text on mobile */
div.header-menu-nav-wrapper>div a:after {
    text-align: left;
}
nav>div.header-nav-item:nth-child(1)>a:after, div.header-menu-nav-wrapper>div:nth-child(1) a:after {
    content: "Asia";
}
nav>div.header-nav-item:nth-child(2)>a:after, div.header-menu-nav-wrapper>div:nth-child(2) a:after {
    content: "Content + SEO";
}
nav>div.header-nav-item:nth-child(3)>a:after, div.header-menu-nav-wrapper>div:nth-child(3) a:after {
    content: "Buy Now";
}
nav>div.header-nav-item:nth-child(4)>a:after, div.header-menu-nav-wrapper>div:nth-child(4) a:after {
    content: "Brand";
}
nav>div.header-nav-item:nth-child(5)>a:after, div.header-menu-nav-wrapper>div:nth-child(5) a:after {
    content: "Us";
}
nav>div.header-nav-item:nth-child(6)>a:after, div.header-menu-nav-wrapper>div:nth-child(6) a:after {
    content: "+1.234.5678";
}

Result: