You can inherit and override the Web Layout View and get some pretty neat effects:

Example View:

< data inherit_id="web.layout">

< xpath expr="//body" position="inside">
     < div>< img src="https://i.imgur.com/0g9YEnF.png" height="77"/>< /div>
     < style>
         .o_main_navbar {
             background-color: #000000;border-bottom: 0px;
          }
         .o_home_menu_background:not(.o_home_menu_background_custom) .o_main_navbar {
             background-color: #000000;border-bottom: 0px;
         }
     < /style>
< /xpath>

< /data>