create anav bar by using flexbox code example

Example: create anav bar by using flexbox

/* Submenu up from mobile screens */
.submenu {
    display: none;
}
.submenu-active .submenu {
   display: block;
}
.has-submenu i {
    font-size: 12px;
}
.has-submenu > a::after {
    font-family: "Font Awesome 5 Free";
    font-size: 12px;
    line-height: 16px;
    font-weight: 900; 
    content: "\f078";
    color: white;
    padding-left: 5px;
}
.subitem a {
    padding: 10px 15px;
}
.submenu-active {
    background-color: #111;
    border-radius: 3px;
}