mainbody.css

header
{
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    padding: 40px 100px;
    z-index: 1000;
    display: flex;
    justify-content: space-between;
    align-items: center;
    transition: 0.5s;
}

header.sticky
{
    background: #fff;
    padding: 20px 100px;
    box-shadow: 0 5px 20px rgba(0, 0, 0, 1);
}

header .logo
{
    color: #fff;
    font-size: 25px;
    text-transform: uppercase;
    text-decoration: none;
    font-weight: 700;
    letter-spacing: 2px;
}

.sticky .logo
{
    color: #111;
}

.sticky ul li a
{
    color: #111;
}

header ul
{
    position: relative;
    display: flex;
}

header ul li
{
    position: relative;
    list-style: none;
}

header ul li a
{
    position: relative;
    display: inline-block;
    margin: 0 15px;
    color: #fff;
    text-decoration: none;
    font-size: 17px;
}

@media (max-width: 991px)
{
    header, header .sticky
    {
        padding: 20px 50px;
        z-index: 1000;
    }

    .menu
    {
        position: fixed;
        top: 75px;
        left: -100%;
        display: block;
        padding: 100px 50px;
        text-align: center;
        width: 100%;
        height: 100vh;
        background: #fff;
        transition: 0.5s;
        z-index: 999;
        border-top: 1px solid rgba(0, 0, 0, 2);
    }

    .menu .active
    {
        left: 10px
    }

    header ul li a
    {
        color: #111;
        font-size: 24px;
        margin: 10px;
    }

    .toggle
    {
        width: 40px;
        height: 40px;
        background: url(Covid\ Images/menu.png);
        background-position: center;
        background-repeat: no-repeat;
        background-size: 30px;
        cursor: pointer;
    }

    .toggle.active
    {
        background: url(Covid\ Images/close.png);
        background-position: center;
        background-repeat: no-repeat;
        background-size: 25px;
        cursor: pointer;
    }

    header .sticky .toggle
    {
        filter: invert(2);
    }
}