Extended CSS:
--------------
#masterMenuSection ul li a {
    background: rgba(255,255,255,0) !important;
    color: #6b0022 !important;
}

#masterMenuSection ul li span {
    display: block !important;
    color: #6b0022 !important;
    background: transparent !important;
    border: 2px solid #000000 !important;
}

#masterMenuSection li.more:hover span {
    background: #e06666 !important;
    color: white !important;
}

#masterMenuSection ul li a:hover,
#masterMenuSection ul li span:hover {
    background: #6b0022 !important;
    color: white !important;
}

#masterMenuSection #overflowMaster li:hover a {
    background: #6b0022 !important;
    color: white !important;
}

#masterMenuSection #overflow li a:hover {
    background: #6b0022 !important;
    color: white !important;
}


.ccs-masterHeader{
	background-color: #6b0022 !important;
}

    .ccs_Header_PageTitleArea > .css_PortalHeading {
        font-size: 32px;
        color: #6b0022 !important;
        font-weight: 400;
    }

    .ccs_Header_PageTitleArea > .css_PortalHeadtingDescription {
        color: #6b0022 !important;
    }

.CCSIsWindowPage #spPageChromeAppDiv {
    background-image: url('https://contoso.sharepoint.com/sites/IT/helpdesk/Portal/SiteAssets/BackImage.jpg') !important;
    background-size: 100%;
}

.CCSIsWindowPage .CanvasZoneContainer.CanvasZoneContainer--read {
    background: none !important;
}


/* By default, a lighter shade is applied for those colors that are added above using .ccs-masterHeader. Below style overcomes that behavior and shows the exact colors.
div#ccs_MasterPageHeader > * {
    background: none !important;
}
*/
Note: Please change the color codes as required.