MyFirstBlog/MyBlog/static/L_header.css

#mainNav .navbar-brand {
    color: #000 !important;
}

#mainNav .navbar-nav > li.nav-item > a {
    color: #000 !important;
}

#mainNav.is-fixed {
    background-color: rgba(240, 240, 240, 0.9) !important;
}