MyFirstBlog/MyBlog/static/header.css

.navbar-toggler span {
    background-color: #1B1B1B;
}

/*--/ Hamburger Navbar /--*/
.navbar-toggler {
    position: relative;
}

.navbar-toggler:focus,
.navbar-toggler:active {
    outline: 0;
}

.navbar-toggler span {
    display: block;
    background-color: #000;
    height: 3px;
    width: 25px;
    margin-top: 4px;
    margin-bottom: 4px;
    transform: rotate(0deg);
    left: 0;
    opacity: 1;
}

.navbar-toggler span:nth-child(1),
.navbar-toggler span:nth-child(3) {
    transition: transform .35s ease-in-out;
}

.navbar-toggler:not(.collapsed) span:nth-child(1) {
    position: absolute;
    left: 12px;
    top: 18px;
    transform: rotate(135deg);
    opacity: 0.9;
}

.navbar-toggler:not(.collapsed) span:nth-child(2) {
    height: 17px;
    visibility: hidden;
    background-color: transparent;
}

.navbar-toggler:not(.collapsed) span:nth-child(3) {
    position: absolute;
    left: 12px;
    top: 18px;
    transform: rotate(-135deg);
    opacity: 0.9;
}

#mainNav {
    position: absolute;
    border-bottom: 1px solid #e9ecef;
    background-color: white;
    font-family: 'Open Sans', 'Helvetica Neue', Helvetica, Arial, sans-serif;
}

#mainNav .navbar-brand {
    font-weight: 800;
    color: #343a40;
}

#mainNav .navbar-toggler {
    font-size: 12px;
    font-weight: 800;
    padding: 13px;
    text-transform: uppercase;
    color: #343a40;
    border-color: #fff;
}

#mainNav .navbar-nav > li.nav-item > a {
    font-size: 12px;
    font-weight: 800;
    letter-spacing: 1px;
    text-transform: uppercase;
}

@media only screen and (min-width: 992px) {
    #mainNav {
        border-bottom: 1px solid transparent;
        background: transparent;
    }

    #mainNav .navbar-brand {
        padding: 10px 20px;
        color: #fff;
    }

    #mainNav .navbar-brand:focus, #mainNav .navbar-brand:hover {
        color: rgba(255, 255, 255, 0.8);
    }

    #mainNav .navbar-nav > li.nav-item > a {
        padding: 10px 20px;
        color: #fff;
    }

    #mainNav .navbar-nav > li.nav-item > a:focus, #mainNav .navbar-nav > li.nav-item > a:hover {
        color: rgba(255, 255, 255, 0.8);
    }
}

@media only screen and (min-width: 992px) {
    #mainNav {
        transition: background-color 0.2s;
        /* Force Hardware Acceleration in WebKit */
        transform: translate3d(0, 0, 0);
        -webkit-backface-visibility: hidden;
        backface-visibility: hidden;
    }

    #mainNav.is-fixed {
        /* when the user scrolls down, we hide the header right above the viewport */
        position: fixed;
        top: -67px;
        transition: transform 0.2s;
        background-color: rgba(240, 240, 240, 0.9);
    }

    #mainNav.is-fixed .navbar-brand {
        color: #212529;
    }

    #mainNav.is-fixed .navbar-brand:focus, #mainNav.is-fixed .navbar-brand:hover {
        color: #0085A1;
    }

    #mainNav.is-fixed .navbar-nav > li.nav-item > a {
        color: #212529;
    }

    #mainNav.is-fixed .navbar-nav > li.nav-item > a:focus, #mainNav.is-fixed .navbar-nav > li.nav-item > a:hover {
        color: #0085A1;
    }

    #mainNav.is-visible {
        /* if the user changes the scrolling direction, we show the header */
        transform: translate3d(0, 100%, 0);
    }
}