Hi Camille,
Thank you for the clarification. To achieve that, please try adding another bar, below the bar with navigation.
1.) Set tha bar height to 9px or adjut it accordingly.
2.) Add the background as white.
3.) On Border Tab, select Solid and set the border color to blue.
4.) On Customize Tab > Element CSS add the following to adjust some settings:
$el{
border-bottom-color: red !important; /*To change blue border color to red bottom part*/
border-right-width: 0 !important; /*Remove right border*/
border-left-width: 0 !important; /*Remove left border*/
}
See this screencasts: https://screencast-o-matic.com/watch/cqif2YO15h
Hope this helps.