Hi Gonzalo,

You can try the font options are salient \ typography - navigation and page header - off canvas navigation.

You can also try this CSS:

#slide-out-widget-area.slide-out-from-right-hover .inner .off-canvas-menu-container li a{
    font-size:15px !important
}

If it does not work then include a link to your site so we write the CSS from the actual site in use.
Thanks. 

Hi Gonzalo,

To make h6 adjustment, go to Salient > Typography > General HTML elements > Heading 6

Hope this helps.

Kind regards,